I was going to make the duct tape preventative suggestion, but someone beat me to it. I also agree that duct tape works well after the fact, and so does just gritting your teeth and going. The only other pieces of advice would be:
Use a good spray-on anti-perspirant, and let it dry, before applying tape. In one test conducted by the US Army, anti-perspirant alone reduced the number of blisters by something like 80%. If you stop the sweat, and don't soak your boots in a creek, that should help.
When wearing two pairs of socks, I use one of the new high-tech wicking fabric socks designed especially as a liner, followed by a purpose designed high-tech boot sock. Places like REI are likely to carry these sorts of items. I'll go on extended hikes with out many clothing changes, except for lots of extra socks. I have learned the hard way that socks matter more than clean undies on a long hike.
When buying a new pair of boots, buy from a store that has a mini hiking trail, or at least a few good ramps, so that you can have some idea of how the boots will perform on a slope. Walking across a flat floor doesn't tell you if your toes will end up jammed into the toe box on a down hill, or if your heel will be scraped raw on an up hill. If you're on a budget, go to the full service store and pick the perfect boots and socks, then order them from a discounter like Sierra or Camp-Mor.
