Learning to see
Much of learning to draw is about learning to see. One of the first things I learned when I started to draw with pencil were contour drawings. In a contour drawing, you take a large pad of paper, put your pencil down on the paper, and trace a complex object without looking at the paper. You trace the object with your eyes, and refrain from looking at your drawing until you are done. The purpose is not to create good art, but to train yourself to look at the fine details of what you are drawing, instead of the drawing itself.
It is important to remember that what we think we see is colored by our beliefs about how the world is. More often than not we are seeing from our memories of how we have experienced the world, not how the world is right now.