draw from life. Take Figure drawing classes. It's the only way to really get better. Look out side. Draw some interesting buildings. Stay in side and draw an interesting angle of your room, hallway, or kitchen.
Basically draw from life. You wont really get this in you head until you do. So that when you draw from your head you'll be able to remember what muscle goes were and how the muscle will look at certain times.
I'm still learning. I'm going to take an outside figure drawing class. Right now my college is being really gay about the illustrative track.