I prefer to slightly stretch the meaning of 'contour' to include lines generally, so that from time to time the line will wander across the form and back out again, capturing little details along the way. Make the line continuous, that is, avoid lifting the pencil from the paper, and most importantly, DON'T PEEK! If need be, work with your sketchbook under the table. If drawing on loose paper, you may need to tape it in place.
Now, just draw your hand! Place the pencil near the bottom of the page, then looking at the edge of the wrist, begin to follow the line, going very slowly and steadily. Try to make your pencil follow every slight curve and bump. When you get to a crease, follow it in then back out to the side and carry on. Don't rush. Concentrate on observing every little detail.
When you've gone all around the hand, stop and look at the end results. Funny? But look how some areas of your drawing are amazingly accurate. Sure, the large areas might be out of proportion to each other, but you will notice that some parts are far better drawn than when you were looking at the paper!