First of all, remember that blisters require three conditions to occur: heat, moisture, and friction. Eliminate any one of those factors and you prevent blisters.
Buy boots that fits
Friction happens when your shoes or boots don’t fit your feet well. Buy them in a store where the staff knows how to measure your foot size. Try on a variety of brands because they all fit slightly differently; find the brand that fits your feet best. If the best boots you find still don’t fit perfectly, try after-market insoles to customize the fit.
Eliminate heat and moisture: Keep your feet dry
This may be the easiest and most effective strategy employed: Whenever you stop for a break of five minutes or more, take off your boots and socks and let them and your feet dry out, eliminating or at least minimizing heat and moisture. As simple as that.
Carry extra socks
If your feet get chronically sweaty, change into clean, dry socks midway through a day of hiking. Try to wash and cool your feet in a creek and dry them completely before putting on the clean socks.
Wear lightweight, non-waterproof footwear
Any footwear with a waterproof-breathable membrane is not as breathable as shoes or boots with mesh uppers and no membrane which also dry much faster if they do get wet. If you’re generally day hiking in dry weather, why do you need waterproof boots? It may seem counter intuitive, but non-waterproof shoes or boots may keep your feet drier because they won’t sweat as much.
Tape hot spots
Carry blister-treatment products like Moleskin—but also carry athletic tape, which sticks well even on damp skin. If you feel a hot spot developing, stop immediately and apply two or three strips of athletic tape to the spot, overlapping the strips, and then check it periodically to make sure they’re still in place.
When you’re taking a really long day hike where you exponentially increasing the amount of friction that can occur, tape your heels before starting out, because you may have developed blisters on them on day hikes longer than 20 miles in the past. If you routinely get blisters in the same spots, tape them before your hike.
Use a skin lubricant
Distance runners have employed this trick for ages: Apply a lubricant to areas that tend to chafe or blister, like heels, toes, or even the inside of thighs, to eliminate the friction that causes that discomfort. Numerous products do the job, from the traditional Vaseline to roll-on sticks like BodyGlide.