I don't know what your routine looks like, but since you mentioned a PT, I am going to assume that he (or she) probably taught you to a safe way to maximize overall fitness, not aesthetics, by which I mean hypertrophy (muscle size).
What was written by posters above about proper form to avoid injury
, diet, sleep and avoiding overtraining (listen to your body) was good. But, if you are like a lot of people I see at the gym, you are not isolating your muscles enough and you are not exercising them frequently enough.
Here are my suggestions -- most of which violate the conventional wisdom, I know, but they're effective:
--Do a total-body workout every time you go to the gym. This is an excellent, but pretty technical, article that explains the scientific reasoning behind this: http://www.magzter.com/articles_new_reader/detail/5187/176029/57df8490c3bb7
. But keep within the range of 2-4 sets for each exercise.
--Go to the gym 3-4 times per week -- maybe more. (Assuming you are getting enough rest between workouts and stretching/foam rolling.)
--Start with your isolation exercises, do compound exercises last, e.g. rear delts before seated rows, bicep curls before lat pulldowns. Proper form to avoid injury
is crucial! Practice before lifting at your maximum. Isolate every muscle as closely as possible and work each with high intensity.
--Keep your reps within the 7-10 range.