You are going back to the gym, now what?

My advice, start slow! The race is long and it is only with yourself. There is no use in hurting yourself because you used to go at a certain intensity. In the beginning, focus more on your nutrition than your workouts, but be faithful in getting your sweat on. As the pounds start coming off, then up the intensity. Remember, killing yourself at the gym without curbing your eating habits is a futile endeavor. Good luck to you!