Always have a contract!!!
Call it a SOW (statement of work), "paperwork," agreement, whatever you like... just make sure you have one before beginning a creative project where money is involved, even if it is with a friend. These boiler-plate templates above are very helpful and feel pretty professional.

If you're not paid for your work that was agreed upon in the contract, it makes it much easier to enlist the help of a collections agency (who will pester your client for you, for a fee - it can also negaively imapct their credit score), or take them to court.

In my experience, collections agencies are easier because you don't need a lawyer, and the process is a bit less involved. Usually if you had a clear contract, and tell the client you will take them to court or pass the debt along to a collections agency, the client usually pays before you even have to get to that step :)