Well, I've found with kittens is that when they bite you, if you say Ow! or No! loud and firm enough to startle them and stop playing with them for awhile, they start to get the point. Then when they don't bite, tell them that they're a good cat. Also, you can gently hold their mouth shut after or as they try to bite you, and say no! If you do it that way, keep playing with them and do that everytime, and they'll get the point, and you'll be surprised at how fast they learn! Remember to always positively reinforce their behavior and don't yell or hit them, and spraying them with water isn't all that great either (unless its the only thing that works, and is used in moderation). I'm not saying you would do this, that's just general advice. I'm always preaching about positive reinforcement, and not using negative tones!
If the cat also scratches while they play, you can grab on to their paw and squeeze just a little and say no. My cat learned so fast that way. Every time they do scratch, just squeeze... its so fun to be able to play with a cat, and have them bat at your hand with no claws, and you don't have to be afraid! I love it.
Hope that helps!
