My daughter cut an article out of the newspaper several years ago about a practice used at Army basic training. It turns out the primary culprit of blisters is moisture, so a good way to reduce blisters on your feet is to cut down on foot moisture. In preparation for lengthy hikes, the recruits spray anti-perspirant on their feet daily for about a week before their hike. After that they only have to spray anti-perspirant once a week to maintain the effectiveness.
I had used this trick on several of my hikes, but forgot to do it before my 2004 Thunder River - Deer Creek hike. On that hike, I had to change my socks midway each day because my feet were sopping wet. On my 2005 New Hance hike, I remembered to use the foot-spraying trick. I religiously sprayed my feet each evening for ten days or so before my hike and then sprayed twice daily a couple of days before the hike. On that hike, my feet were completely dry all five days. I got absolutely no blisters.
In addition to the foot spraying, there are a few other things I do before each hike. I carefully trim all my toenails and shave off any hair that might be on top my toes.
If you have trouble with bruised or black and blue toenails, you might try the following: cut out four one-inch wide strips of Moleskin Plus Padding about three inches long. Wrap the first strip on top of your big toe, across the front of it, and down under the big toe. Then wrap the second strip around your big toe going completely around it and the first strip. Then complete this process for the other big toe. This way your big toes are completely wrapped in Moleskin. This helps to cushion your big toes from the downhill descents and helps to prevent any blisters from forming on the big toe or the second toe. However, the most common cause of bruised or black and blue toenails is boots that are too short. Most experts suggest your boots be one-half to one full size larger than your regular size to allow for some foot movement.
I always wear a fresh, clean pair of polypropylene liner socks and synthetic socks for each day's hike. I personally use the maximum weight Thorlo hiking socks (# 3 padding) for my outer socks. They are pricey, but my feet are worth it.