One of the most common injuries for runners seems pretty innocuous on the surface. No bones are broken, no ligaments damaged. Still, anyone who's had a significant blister can attest to how strongly the pain they inflict can affect your running. The changes in running posture caused by this pain can easily lead to additional injuries. It's a dark road you don't want to explore.
Blisters are damage to the skin, usually from friction and too much moisture [source: Mann]. If you fall victim to one (or more -- they often like to come with friends), don't try to break the blister. As tempting as it is, it could lead to infection. If it's already broken, sterilize the area and apply a bandage. Unbroken blisters will heal on their own if you leave them uncovered.
Prevention is simple. Wear socks that wick away moisture from the feet, and use shoes that fit your feet properly. Like most running injuries, not overtraining will go a long way toward your goal of never seeing another running-related blister.