Sometimes you get clients who are amazing. You almost feel bad making them sign a contract. However, occasionally there is the client from another planet who will run you into the ground. For these special situations the best way to guard yourself is to have everything in writing and signed off on. Even if you feel like you might be best friends in the future, a contract will save you from any messy situations that should get in the way of getting to vacation together later in life.
Here are a few things I like to make sure I include to save my tush! (these are all suggestions from a graphic designer, take and leave what makes sense for you)
1. Timeline : this keeps everyone's expectations on the same page.
2. Round of Edits : so important as you can end up doing far more work than initially quoted. Bad for you and your client's checkbook. This can include mood boards, sketches, formal designed drafts and then how many edits they get after the design is chosen.
3. Ownership : who owns the final product. For my situation the client owns it but I have rights to use it for personal publicity, I also state who has rights to change things after the hand off happens, do you want another designer to be able to edit if needed or not? **this is especially important if you're bidding on a project and have to show sketches, you don't want someone to hand off your intellectual property to another design who promises to finish it out for less than you.
4. Payment : when do you want to get paid? You can ask for partial payment upfront and the rest at final hand off. Or all at once. Consider putting a clause in that protects you if the project gets canned 25%, 50% or 75% of the way through. You've put time in, if you worked in corporate you would just move on to the next project but have gotten paid for your time already.
5. Reimbursement : who is responsible for cost of fonts, outside artwork or illustrations, photography, copy writing etc.
* I also always contact the client if I feel like cost will change or once I know cost of fonts just to confirm it's in their budget.
If you're really stuck do a quick search for example contracts in your field or find a helpful book, there are so many out there it's worth the work of finding a good one and not getting yourself in to a mess. The less mess the more you'll enjoy your work and your client!