Cartoonist and illustrator extraordinaire Tom Richmond has an excellent in-depth guide to drawing hands over on his blog. As per usual with Tom’s instructional articles/blog posts, he goes into far more detail and insight than one could possibly imagine he would have time for, even down to supplying illustrated diagrams explaining everything.
Here’s a quote demonstrating the level of insight you’ll find:
Many people think the knuckle of the finger rests directly behind the crease that represents the base of the finger right under the bottom finger pad. Now turn your hand around. That main knuckle is SIGNIFICANTLY lower on the hand. In fact it’s below the upper pad of the palm that curve below all the fingers. A lot more of your finger resides inside the palm/body than you might think. Understanding that is a big part of figuring out hands.
At some point I can see Tom collating all these posts into a book of some sort. His blog tutorials are better than any book on cartooning I’ve ever seen, and this one is no different.
Probably one of the more difficult parts of the human body to draw, and Tom is a master at the cartoon hand. Head over there and learn from the best.