How to prevent blisters?

This Oxfam Trailtrekker challenge has really led me to seek ways as to how to prevent blisters. The last few long distance walks I've been on for training I've ended up with loads of blisters (more like growths than blisters actually), well I call them long distance walks they were only really 20 some miles so they probably don't fall into the long distance walk bracket but for all intents and purposes I'll refer to anything over 20 miles as long distance (no doubt something the LDWA would dispute).

The blisters I've had have been the most agonising part of the walk and where I've felt my legs can do more the blisters definately can't thus I am embarking on a quest of research to find out how to prevent blisters to ease the pain particularly for this gargantuan yomp we're having a shot at. Any techniques or ideas as to how to prevent blisters must be a bonus on the day.

I've started my quest with a rough search and already came up with what seems to be a good broadbrush start here.

Other "How to Prevent Blisters" posts
Correct footwear to prevent blisters
The secret weapon in how to prevent blisters
Look after your feet to prevent blisters
How to prevent blisters on the day you walk