The easy answer is this: make a contract that benefits you as much as possible, and get them to put down as much as they will. Don't worry about the client because they'll tell you when they want to negotiate something.

The hard answer is: it depends on the the client, and you need to get an attorney who knows about these things. If you aren't hard up for business, you can play tougher. If you really need money, you'll have to agree to things that are more in favor of the client.

I wish I could find this perl program I used to have (have only, I didn't write it) that acted as the contract. It spit out the postscript for the thing you printed. It was more of a novelty, but it impressed a couple of clueful clients.