5. Set the cuff angle.
If the angle of the cuff relative to the lower boot is not set properly, the ankle joint will be ‘turned’ one way or the other once the boot is buckled. There are two reasonable ways the layperson can evaluate this without fancy equipment.
First, walk in a straight line on a hard surface. Try not to think about how you walk, but be aware of how your boot soles strike the floor. They should strike more or less flat. If they strike on either edge, tilt the boot cuff until they strike flatter. If your boots do not have an adjustable cuff, or if there is not enough adjustment available, you can artificially increase the volume of your leg on either side by making a shim out of any non-compressible material. Folded trail maps work well for this. Eventually, you should remove an ankle rivet, tilt the cuff, and secure it with a t-nut assembly.
The second method is to pick your booted foot off of the floor, and see if you can invert and evert your foot easily. If one direction seems harder, or significantly less mobile, adjust to equalize.
It is worth noting that if you have oddly shaped ankles or curvature of the lower leg, it may be necessary to modify the shells or liners to fully restore ankle mobility. My medial anklebones are fairly protuberant, which means I have to spend a significant amount of time with a press and heat gun. ‘Significant’ here, is counted in multiples of hours. If, upon removal of your boots at days end, you notice the red hue that follows pressurized flesh on either medial or lateral anklebone, let that be your clue that something is amiss.