It may heal itself. If the fluid isn't absorbed in that time, puncture the blister using a sterilized needle and drain the fluid. Always be careful to preserve the outer skin, which will protect the blister. Then apply Vaseline or Preparation H and cover with a gauze pad or bandage, or try a specialized new Band-Aid product called Blister Block. If you get blisters often, you may need to change shoes or try a commercial insole such as those from Spenco, Sof Sole, Dr. Scholl's or Sorbothane.
Insoles can help reduce the friction that causes blisters.
The foot needs strength-training like much of the rest of the body. If the muscles are weak, they will not move the foot into its proper running position. The foot flops around instead of pointing straight ahead. Also, the stronger your foot and leg muscles are, the faster they can propel you forward. The simplest way to strengthen your feet is to kick off your shoes and go barefoot whenever you can.