1. Put your boots on at home, and tie them as tight as reasonable, but with a single bow-knot. This allows the heat of your feet to stretch and conform your boots on the way to the trailhead -- and has the added benefit of not letting you forget your boots at home!
2. Once at the trailhead, re-tie your stretched, warmed-up boots, again as tightly as reasonable, but snugly - not tight. You'll be surprised at how loose they've become on the drive! Do this with your foot at a 90-degree angle to your shins, and the soles of your boots flat on a hard surface. The back bumper works, or a rock, or whatever. Do NOT kneel down to re-tie your boot, as your shin will be pushed forward, and result in a loose fit.
3. Tie the knot in a double-knot, which will likely last the entire day, and not require you re-tie your boots on the trail, where you are likely to tie them TOO tightly.
In my experience, using this method to ensure a snug (but not tight) fit when you actually hit the trail removes most of the friction motion that leads to blisters -- especially on the back of your heels.
I have no advice for people who hike in those goofy slipper thingies with toes, however....
-Tom
) can cause problems. 
And those aren't exactly the friendliest things for my feet and lower legs. They're nylon, over-the-calf style socks. That's better than cotton, but they're too thin for hiking. And they're the heaviest compression available (30-40 mmhg) short of custom prescription socks. 
