Please re-read my initial comments about boot size and lace tightness, as that will fix 98-99% of all people who have trouble skating.
Of course if you have a sports podiatrist who understands skating boots, their advise is much more important than mine. I'm not an expert, but am only trying to learn from the mistakes of a fitter who fit me wrong, and from other people with similar problems.
Your next step is to determine whether the boot is too large or small. If you are still growing, or your weight changes (or your fluid content alters due to natural body cycles or pregnancy - adult ladies especially take notice), you may find your feet change with time, so this may need to be redone periodically. For speed skates, there are inner liners which can be changed or removed as a child grows, but I don't know of anything similar for figure skates, though Riedell has sold some boots that are adjustable in size. Re-heat molding boots can stretch them a little. Unfortunately, people who buy extra large boots to accomodate a child's growth are often disappointed - the extra size causes the boot to break down even more quickly than the child grows. In the mean-time, the child has trouble skating, and may get blisters.
The nominal "length of the boot" seems to be the length of the outsole, from heel to front. Skater's Landing appears to indicate that the length of the outsole should be the length of your foot on the floor, from heel to the farthest forward toe, measured the main axis of the foot. See the diagram there. However, that could only be true on full custom boots, shaped exactly to your feet. And that might mean you would need different lengths for your left and right foot. In reality, full custom boots are expensive and take fair amount of time to get made. So in order to not be too narrow for the foot width and bend at various points, and in some cases the tendency of boots to narrow at the heels and toes, and in order to get the same size on both feet, most people end up with longer boots than feet.
Since the length of the outsole is picked by most skate techs as the same or slightly longer than the length of the mounting plate of the blade (which is not the same as the length of the blade runner at the bottom of the blade), I think this means that most skaters end up with blades that are too long for good skating.
All the skating boots I have seen have a sole that is too rigid for there to be significant motion of the foot inside of it - presumably to prevent blisters and other foot injuries, and in order to keep good control over the position and orientation of the blade. (The outsole at the bottom of the boot must be rigid so as not to warp the mounting plate of the plate, which in turn could warp the blade runner itself.) That is only slightly modified by using insoles at the bottom of the feet that have a little give - e.g., I usually cut my own foam insoles. That differs substantially from street shoes, athletic shoes, hiking boots (in all of which the heel sometimes lifts off the back of the insole), and some types of dance shoe. In terms of lengthwise bend, most people can only bend their feet much in the joints of their toes, and at the center of the (hopefully well padded by various material in the foot) "ball" of the foot, around the back of the "metatarsal" bones, which lie behind the toe bones. (The "Head of a metatarsal" refers to the back end.) It appears to me that ballerinas and other very flexible people, can sometimes bend their feet along other points of their foot. Nonetheless, it probably still makes sense to go with rigid soles and place the bend at the center of the ball.
Many expert fitters say that the most important length is the length of the unbent portion of the foot at the back, measured from the back of the heel to the ball of the foot. That's because in almost all cases, the boot bends upwards at the ball, to try to prevent your feet from sliding forward and back. But if that bend point is wrong, there is a lot of stress on your feet, which could easily cause both pain and severe injury. Unfortunately, most boot manufacturers do not list that length!
Another important factor is the angle of that bend. It should not be so great as to be uncomfortable, let alone injurious, nor should it imbalance you much. That is associated with the (internal, not external) height of the heel. Most fitters do not consider this angle. In the case of my nominally full custom boots, it was far too great a bend.
Because most skaters don't know the dimensions of their feet, they try to pick their skating boot size by what feels comfortable in street shoes, athletic shoes, or hiking boots. If they had full custom shoes, that might be the same thing, though in some ways it is better for those shoes to be a little loose. Here is a good source on the sizing recommended by various skate brands.
That said, I would personally prefer to start with boots that are fit a little loose to boots that are fit a little too tight, because stretching ("punching") leather tends to be temporary, often lasting as little as a few weeks, especially if you need to stretch the boot a lot, as you might in some spots if you have parts of your foot, like heel bones or toes, that stick far out relative to the initial shape of the boot. But that assumes you make modifications of the type we have indicated in these pages. Otherwise, loose boots will cause so many problems with control and blisters, that loose boots are a very bad idea.
You need a boot that hugs your heel, has the bend in the foot bed where the ball of your foot is, with an amount of bend that is both comfortable and lets you feel in control of what your skate is doing. As much as possible, the boot should be snugly comfortable all over. The the overall length of the boot is almost completely irrelevant, because the front of the boot does not touch the ice. (NOTE: as mentioned later, most fitters size the blade by the length of the boot outsole. So an extra long boot leads to an extra long blade. I believe that's just plain wrong. Make it the same length as your foot, or slightly shorter.) A really, really long boot would be a problem in the sense you couldn't bring your feet close together (though it would still look like you could), but I think you would know if that was an issue. Those things you can easily check.
The "Brannock Device" is the common device for measuring foot length and width. There are a variety of different such devices for different brands of skate boot. They are used to estimate stock sizes, but are insufficient to fully measure the 3D shape of the foot.
Bauer sells a 3D foot scanner, that can be used to size Bauer brand (hockey) skates. But figure skate makers can't use the results. I don't know anything about them, but based on that video, it doesn't really do a full custom fit, and don't get the full bottom-of-the-foot profile, but merely picks the closest off-the-shelf Bauer size. Based on other pages, they base the 3D shape on shots taken from multiple angles. But it's a cool idea.
It is a good idea to tighten in two passes, and to start at the very bottom. I leave a little slack at the very bottom in the first pass, and remove the slack from the rest of the laces. Then I go back to the bottom, and make it very tight. It is much easier to pull laces through the lace holes if you pull straight out than if you pull upwards and outwards. Some people who pull upwards at the same time find the lace cuts into their fingers. If you drop the tension on the lace for even an instant during the final tightening, such as when you switch hands to lace opposite sides of the boot, all will be lost. Instead, when switching hands after you have pulled the lace through, pull upwards, then pull inwards, to draw the sides of the boot together.
Tight lacing can be done by using one finger to lock the lower part of the lace onto a hole or hook while using the rest of your hand to pull the lace just above the hole or hook. It's awkward to do this with your hands, so some people prefer to use "lace pullers" - hooks that some shoe stores sell for about $1. Or you could buy a reasonably sized hook for hanging stuff from a wall at a hardware store - you could tape the sharp point on the screw at the other end.
Many people find it easier tighten to use waxed cotton (non-elastic) laces, which don't slip as easily. This is probably a good idea if you have finger coordination problems, and are unable to tighten nylon laces enough. I don't use cotton laces because if they slip even a few thousandths of an inch, they lose their tension. Some people say cotton is prown to sudden breakage, when it wears out. I prefer nylon laces, which are somewhat elastic, but opinions differ. Nylon laces are slightly more slippery, and may be slightly harder for some people to hold and tighten. Some boot laces are wider than others, and are therefore easier to hold without slipping. I've used the wider ones. Nylon/Cotton blends represent a compromise. As far as I know polyester laces are comparable to nylon, but may be a little less strong and more flexible.
I have now switched to a good quality 3 mm nylon utility cord, also called parachute cord, like this, of the type commonly sold in the climbing rope section of outdoor gear shops. (But it is too small for climbing, and not rated for that.) It is round, which makes it much easier on your fingers to pull tightly on, and it doesn't twist. The kermantel construction (innor solid core for strength, outer braided shield to protect the cord) means it lasts virtually forever. (However, like anything, they get dirty, so after a few years, I replace them anyway.) I slightly melt the ends with a match, then roll them to make a thin tip that threads through the holes easily. (Be sure to have water on hand when you melt it, because it is flamable.)
I've claimed boot makers should replace all lace holes and hooks with jam cleats, so one could adjust range of motion and resistance everywhere separately. This would also make it easier for people with coordination or arthritis problems to tighten their laces. I don't know of any figure skates of that design, nor do I know of any with ski or hockey boot style buckles, which would be easier to tighten. But there used to be sold LaceVice (website no longer works) looked like a device that sits on top of your tongue that contains simple cleats to let you tighten different levels of the lace to different levls of tightness. One person said it also helped them when the tongues of their boots were too soft to prevent "lace bite".
Jackson ProFlex boots (no longer available) used a ratchet system to tighten a cable instead of laces. You can easily draw them very tight, but the tightening knob may get in the way of footwork, and some say the mechanism is failure prone, and quite difficult to repair.
We have emphasized a snug boot fit throughout these pages. But don't use such a tight fit or lacing that your feet tingle or you cut off sensation or circulation, or you could lose your feet! This is especially likely if you have "diabetic feet" or any other type of very poor circulation problem in your feet, or have trouble feeling tight or loose spots on your feet (neuropathy). It is often said such people should avoid tight footwear, so it is possible some such people should not skate, or should only do the very low level skating possible with soft relatively loose fit boots. If in doubt, consult an appropriate physician, such as a podiatrist.
Boots are generally smaller higher up on the boot. So, to make more space, remove the insole completely, or use a thinner insole. Very thin socks help. To make less space, use a thicker insole, or add in a second insole. Unfortunately, thick socks tend to shift and slip, so may not be a good idea.
Make a new insole by tracing the old one on top of a piece of leather or felt, then cutting to the same shape. This helps prevent the insole from sliding around.
Glue together multiple thicknesses if required.
Keep the old insole so you can repeat this step when needed.
For the most part, boot makers make insoles out of incompressible materials like leather or felt, so I have suggested the same. But some boot makers now make insoles with squishier insoles, and boot makers sometimes use somewhat squishier materials to reduce inflammation (and its side effects, such as the growth of bone spurs and fragments in the middle of joints) on skaters who jump. If you prefer squishy insoles, buy cheap (e.g., $1-$2) foam insoles from the local drugstore, and trim them to match the size of the current boot insoles. Expensive insoles offer no advantage. However, I have found that for me the soft squishy insoles do not keep my feet particularly comfortable, especially with heavy use.
As mentioned here, I have personally switched to using closed cell foam from camping mats, like this. It is warmer (which I like) and lasts a moderately long time. But I have to cut it to 3 dimensional shape with a sharp scissors. That took some practice to learn; using tape is faster to learn. Every few months of skating I have to replace it, because it mats down. Some people use other foams, like heavy closed cell urethane foam (covered with moleskin to be skin safe), which mat down more slowly (so they last longer), but I haven't tried that myself.
Some people skate without socks (though that breaks down the leather a little faster), to gain better control, or to make more space. The skin is much more sensitive and likely to develop problems if you do not wear socks, and the boots will stink. (Foot deodorizers may help.) But thick socks are a bad idea, because they are too squishy, and they generally let your foot slide or roll around, leading to a loss of control, or to blisters. If you wear socks, keep them thin and incompressible.
Socks have an interesting advantage if you want to very quickly try out simple modifications to take up space, or change the distribution of pressure on different parts of your feet, without having to remove and tape the insole or boot interior. You can roll up paper towels and stick them inside the sock where you want them. But paper towels (such as come from public restrooms) are usually more abrasive than socks, so you must make sure you have enough pressure that the foot won't slip against them and make a blister. This may also be a great quick reversible way to convince someone that selectively taking up space can solve a lot of their skating problems.
You can make the insole wider than the original in places. The insole will wrap around to the sides of your feet, reduce the effective width. ("Wings" are my made up term for this.) This can also widen a rigid orthotic, so that it fits tightly and cannot rock, but don't make it so wide it widens the boot. Warning: I excessively widened my old boots at the bottom by using a rigid Superfeet brand moldable pseudo-orthotic insole. (Not the same thing as the flexible SuperFeet insoles, which might or might not fit your feet.)
Blisters are almost always caused by laces that are too loose or boots that are too loose at some point. So are some calluses and corns. (But, blisters, calluses and corns on the front and sides of toes indicate there is excess contact and/or sliding there - which there should not be.) But other factors can contribute, such as moisture and sensitivity to the chemicals used to manufacture the boot. In my case, skating without socks led to the development of corns and calluses, which went away when I returned to socks again, so I am probably slightly sensitive to the chemicals in my boots. If you get the fit right, blisters, calluses and corns rarely form. Of course, if you prefer to keep a little room in the back and front of the top part of the boot (as many freestyle skaters do), you do not have the type of fit that will prevent blisters, so you will have to cover the areas where the boot can slide against your foot or sock, as described below. (With that style fit, you will also have to accept a greatly reduced boot lifetime, such as 3 - 6 months instead of 2 - 10 years, because there is room for a breakdown crease to form.)
If blisters break, then follow standard first aid advice: e.g., as with any open sore, wash and disinfect them, and perhaps use antibiotics, before covering them with something sterile.
Cover the area with something so blisters don't reform or get worse. I used to use Band-Aids (or other brand sterile adhesive strips). You can wrap a little sports gauze instead. Someone on skatingforums.com wrote that she had used "a non-woven, hypo-allergenic [medical] adhesive tape that used to be called Hypofix. It is a thin, papery tape that comes in different widths. Because it is thin, it doesn't cause her problems with bulk, but protects the area." Many people use gel pads, such as those made by Silipose.
I generally carry the paper first aid tape (which has a very weak adhesive) from a dollar store and use it instead of both the sterile cover and the sterile adhesive strips. I'm not sure how sterile it is, but it works well enough for me. (Together with cloth first aid tape in case I need to reinforce anything or attach something as a splint, and alcohol prep pads, and sometimes antibiotic pads, that is generally my entire outdoor excursion first aid kit for anything. Though if I might need to other people, I might carry gloves, and an N95 or KN95 mask for CPR, and maybe feminine hygene pads to absorb blood. For the most part, other first aid items are largely superfluous at my minimum level of training.) Though I rarely have foot problems anymore now that I've done these various things - the paper tape is now mostly in case I fall while not wearing gloves or long sleeve shirt, and scrape my skin.
Bunions, which are sideways bends in the feet around the toes, are more controversial in how they form. But one common theory is that there is excess pressure on the sides of the toes, where there should be little or none.
If an injury appears serious, consult a physician.