From a well known backpacking magazine:
1. Insist on a good fit. Look for boots with a snug heel cup, a secure arch, and plenty of wiggle room in the toes. Heels shouldn‘t move more than 1/4 inch as you stride about the store. Be sure toes don‘t bump into the fronts of the boots on descents.
2. Wear trim-fitting socks. Socks should hug feet, not sag or bunch. Never wear cotton socks or socks with bulky seams. Wool is the material of choice for cold-footed hikers, but hot-foots would do better with synthetic blends.
3. Break in boots slowly and completely. Wear them around the house and town, gradually working up to all day. Break-in time depends on the stiffness of the boot. Lightweight boots can be tamed in days, but all-leather mountain boots need weeks of wear.
4. Nip "hot spots" in the bud. The instant you feel one, slap on moleskin, duct tape, or petroleum jelly to reduce friction. Have a professional boot fitter soften and/or stretch areas in your boots causing hot spots.
5. Minimize foot movement inside your boots by using a better lacing technique or inserting a different footbed. The less your feet slide forward and back, the better. A contoured footbed will do the job also.
6. Keep feet dry.
7. Keep feet clean. At the end of the day, scrub them with clean water, and don‘t forget between the toes.