Hang in there and keep playing. This was me the first few weeks I had the game. I was getting blasted by the computer and by my buddies. After taking my lumps, I started to get better and better. Now I got some good win streaks going vs. my buddies.
Changing over using the shot stick instead of the square to shoot seemed to help me out. It helps with open jumpers, but also on a fast break moving around a defending in the middle underneath the hoop.
Also this game is all about shot selection. You have to find the open spots on the floor and take shots from there. Taking shots with a defender in your face will make you shoot bad percentages. I know this might be common sense, but working the ball and being patient is the difference in the game. And be careful with the passes. Those long passes look so tempting but result in turnovers.
Use the quick plays, post up is good. Use the Pick and roll, although they hardly roll. But you can use the pick as a screen, and use it as a pick and pop a shot.
Also what helped me is practice mode post play. With 2 on 2 you can practice some iso motion moves with your guard, and post moves with your big men. I've got a real good post game now, love working the paint and the ball down low.
Learn a bunch of teams, their players, and their shots and you will keep improving.