Take rest days especially after a long run or your "heavy days" of training, Dr. Steinberg advised. For most beginners, he recommends only running about three or four times per week. If you wake up sore and you're feeling better after foam rolling or stretching, you can train, but sharp pains are definitely a warning sign. "You've just got to be mindful and listen to your body," he cautioned. Other things to remember along the way include nutrition, hydration, and sleep. Sleep deprivation can be very harmful to training, he said.