In reply to UKC Articles: I'm lucky enough to have epidermolysis bullosa simplex, which means that one of the proteins which attach the epidermal layer of skin to the dermal layer below are defective. Needless to say this means I can blister fairly easily, which has allowed me to refine my blister prevention skills!
As jwhall pointed out vaseline is good, I have gone out with my shoes or boots squelching underfoot which is an odd feeling but seems to work.
Another less extreme approach which I did not see mentioned is using antiperspirant and talcum powder on your feet to combat the dampness caused by sweat, on a hot summers day this is a lifesaver!
For heel blisters as well I have found 5x5 dressings taped on using micro-pore to be very effective.
Another recommendation is silver socks of various different brands. Pricey, and I don't know why they work, but they do. They are at any rate antimicrobial which stops odor and may help preventing infection in those that have inevitable popped.
I'll admit I do lance blisters, but there are those where this helps, and those that you definitely do not want to lance. I've just figured this out the hard way by trial and error. The hard and excruciating way.
Without this advice and the advice in the article in the summer I could probably barely walk 2 miles without getting blisters, but as it stands I can prevent them well enough to run half marathons and enjoy good long days in the hills.