Learning to see

I know I've said this thousands of times, but the most important thing you can do to improve your drawing skills is to learn to look, and draw what you see not what you think you should see. The second most important thing is to practice. You should be using your sketchbook every day, drawing people and actual objects around you in lots of different media (pencil, pastel, charcoal, crayon, pen etc.) If you can't actually draw somewhere practice your observation skills. Look at items around you, notice shadows and highlights. Where is the light source? What is the texture like? How would you draw it? I just found a site with good drawing lessons that can be downloaded or viewed online. Here is a good one to start with:
www.drawspace.com/lessons/view/b11 and a sample image from it: