The biggest mistakes people typically make when working out are that they are not following a set plan, they don't schedule their workouts, and they keep doing the same things all the time without ever getting someone to teach them how to lift properly.

All of these errors will result in less than maximal results, no matter what your goal may be. The point of lifting weights is that you are giving your body stimuli to grow and get stronger. In order to do that, you need to be progressively increasing the weight week by week.

Focus your attention on using large movements that create the best responses, like squats, deadlifts, dips, pull-ups, shoulder press and rows.