Tape a piece of drawing paper to a table or desk. Place sections of tape around all the edges to keep your paper still.
Position yourself in a chair so that you are facing sideways at the table or desk, not looking directly at the paper or desk. Point yourself the opposite direction of the hand you draw with. For example, if you are right-handed, point yourself to the left of the table.
Hold a pencil in your drawing hand and place the point on the paper. Hold your other hand out in front of you.
Focus your eyes on the base of your hand where it meets your wrist, but do not look at the paper.
Follow the edge of your hand with your eyes and move the pencil in tandem with your eye movement. Do not look at the paper until you have followed your entire hand. The reason for not looking at the paper is that the left part of your brain needs to rest, while the right part of your brain works with your eyes and hand to create the drawing. Looking at the paper will interrupt your creative thinking and allow the left part of your brain to stop the process.
Practice this technique until your brain learns to recreate the shape of the hand.