Wearing the right pair of sports socks is your number one blister control tactic. Without them, your feet are subject to big time friction. Thin with good moisture management and high durability are must-have features for happy feet. (There are some exceptions to this rule. For example, I recommend wearing thicker socks with hiking boots.)
The socks you wear should conform perfectly to your feet; no wrinkles, bunching, or extra folds. I prefer synthetic materials like nylon because they dry quickly and hold their shape. For example, I’m a huge fan of PowerSox. I wear the ones with an anatomical performance fit; as with shoes, there’s a left sock and a right sock to give you a customized fit.
One old marathoner’s trick involves slipping on knee high stockings underneath your socks. The socks slip against the nylon but the nylon conforms to your feet. I admit this is a little odd, but I know some hardcore road warriors who swear by this method. So if you’re really suffering, pride be dammed.
Gooping up the feet before a workout is an icky affair but it's effective. Petroleum jelly works fine, but I think products especially made for blister prevention work better. I personally swear by Lanacane Anti-chaffing gel.
If you’ve got recurring hot spots, try placing some athletic or duct tape over the offending area. You can also look for a bandage such as Blist-O-Ban which has laminated layers of breathable plastic film and a self-inflating bubble you center over the blister. When your shoe rubs against the bandage, the layers slide smoothly against one another rather than your tender skin.
If your blisters balloon up anyway, visit your doctor or try draining them yourself using a sterile razor blade or nail scissors. (Now that I think about it, just go see your doctor!) You can also cut a hole in an old pair of shoes over the corresponding area so your blister has nothing to rub against. This should eliminate painful friction and allow the blister a chance to heal completely. In the meantime, toughen up the area by painting it frequently with a liquid bandage.