As I tell, If you are thinking to draw something then at first think what you want to draw. Then give relax to your mind, after start to make an image negative in your mind. After you start by pencil and make an image which will no correct image as we know. But you need to try it, after few times try then only it will around 80% correct image, what you thought. Like this if practice then you can be archive your goal. By the way thanks for comment