A couple of things that could help you to improve (at least i like to think that they help me ):
I use the web quickposes to draw figures' shapes/poses. You can set diferent intervals of times to draw them, so you don get lost in the details, and is something nice to do even as a warm up exercise.
1x1 minute image.
Look at an image during one minute, close or hide it, then draw it during other minute. It's not about draw the image to look like the original. The idea is to focus in the part of shapes, forms, perspective, etc.