Learn how to sketch by ignoring your eyes

I know what your saying and that is hard to do because need you eyes in order to draw. But what I really meant by it is that you eyes are tricking you into thinking that there is something there when there really isn't

Let me clearfy it again The visual processing that is going on in your brain The reason why your brain tricks you into thinking something different is because It needs something to help it understand what you are looking at. for example: imagine your looking at a table and you wanted to draw it by using the visual perspective the top of it is flat, it's round and straight sides right? Wrong ! your looking from the envisioning it from the top and looking at it from the side.
Try using the visual Perspective (of your viewpoint)

You see your brain plays a lot of tricks like that. Those tricks affect how you affect how you judge the size of things, the distances from one another, their shading. It's called drawing on the right side of your brain.

i would like to recommend getting a good book on this where there is a wealth of knowledge to help keep you sharp as artist. It's called Drawing On The Right Side Of Your Brain By Betty Edwards . I believe it's top best sellers and can help you understand and open your way of thinking to a whole new level.