Resting is just as important to your training as running. Running every single day doesn't allow your body the time it needs to recover from the workout. Repeatedly over-taxing your body can result in injuries such as stress fractures or shin splints, both of which can have you out of the race for a while [source: The Runner's Guide].
Hydrating is equally crucial. The more you exercise, the more you need to replace the fluid lost through perspiration. For normal exercise, water should do the trick; for more intensive workouts (more than an hour), consider a sports drink containing sodium. Keep drinking even after the workout's over to keep your body properly hydrated [course: Mayo Clinic].