A Confidentiality Clause
If your programmer spills the beans, he gets twenty years in a Turkish prison. That would be nice, but non-enforceable. A financial penalty is enforceable though and par for the course in a work contract.
The information you share stays between you. If the programmer tells someone else and you lose money, you want to be sure you’re going to be compensated.

Payments
If this is going to be a cash job, you want every penny put down. You don’t want to release your product, watch it make millions then get hit with a lawsuit from your old buddy claiming 50% in royalties. If you’re paying, the product is yours and so are the profits.
On the other hand, if you’re not paying, the product isn’t yours. If you’re working on a profit-sharing model, you’ll have to negotiate who gets how much of the profits and for how long. And you must be sure that that’s all put down clearly in the agreement.

Timeline
Creating a software product can take a fair bit of time — at least several months and much longer for really complex programs. Before you write the contract, ask the programmer to tell you how much he thinks each section is going to take and include those in the agreement. You could even put in penalties for failing to meet deadlines, just as you would if you hired someone to fix your house.
In my opinion though, it’s better to be flexible about deadlines. All sorts of unseen problems can crop up while you’re putting together a program.

Maybe you’ll have some changes; maybe the programmer will have some suggestions and these things might have an effect on the timeline. As long as you seem to be heading towards your target release date, and as long as your programmer isn’t stringing you along, I advise being flexible about the scheduling. It’s better to get a great final product than a quick one.