Start your back workouts with hanging-chins on the pull up bar. If you can't do hanging chins, try to just do regular pull-ups. Once you work your way up to weighted hanging-chins (with good form) you should notice some decent development. Depens on how heavy you are. I like to do stupid heavy one arm dumbell rows as a second movement. I break my back workout up into width/thickness/width/thickness/detail/detail movements. My favorite detail movement right now is a seated low cable one arm row for high reps.
Hanging-chins: Grasp pull-up bar with a pronated (Hands-foreward) grip, pull your body up until the bar is below your chin or up to your upper chest, lower body slowly with emphasis on controlling the motion, stop just before extending your shoulders (don't just let your weight hang), pause for a 2 count, repeat. If you can get 12 reps, add weight until you struggle for 8-10 or less depening on your goals.