An under inflated tire runs hot due to the action of the tire as it rolls under the car. The sidewalls become squashed outward, and it is this movement that causes the tire to generate heat, and thus, cause the tire to fail. Regular rotations will help improve tire life and insure an even wear pattern. Tire rotations should be done every 6,000 to 8,000 miles. If your car has directional tires you will want to keep them on the same side of the car rolling in the same direction.
Directional tires have an arrow on the sidewall and are usually specified as directional.
While doing these rotations, tires should be inspected for unusual wear such as more wear on one side than the other. Unusual wear warrants attention at your local alignment shop. Out of balance tires can cause unnecessary wear on vehicle suspension due to excessive vibration, and they won't last as long as they should. New tires should be balanced when first mounted, and when re-mounted due to a tire repair or at the sign of any unusual vibrations. It is also a good idea to have them balanced halfway through their tread life.