It depends on what your goals are and the pace and time at which you run. If your goal is weight loss, running as fast as you can for 30 seconds followed by 1 minute walking/slow jogging and repeating for 15-20 minutes would help you reach that goal. If your goal is to be able to run long distances, then the only way to train for that is slowly build up the distance you can run each day. For instance: day one: jog a half of a mile, day two jog a mile, day 3 jog a mile and a half, day 4 jog a mile, day 5 jog a mile and a half, day 6 jog a 2 miles. Follow that progression, and assuming your nutrition is good, you'll be up to half marathon distances within 3 months. Also, I always recommend that people use some sort of resistance training, either with bands or dumbbells, in order to preserve muscle mass.