Well first of all, it helps to know how the hand is broken up. Here's a quick photoshop mouse drawing showing some major muscles. The blue lines show where the hand folds, and the red show how the fingers all connect. It's not anatomically correct as in every bone is in the right place, but it's how the hand is basically set up. The green lines show how the finger joints usually line up.
Check out your own hand and you'll see that things line up just like that. You can feel the big muscle in your palm, you can see the folds in the form of that M thingy. Just basically know how things are made up and you'll be alright.
