Use A Contract
Using a contract is important. A contract (aka deal memo, statement of work, and booking agreement) provides transparency about the scope of work and payment terms for both you and the hiring party, serves as proof in the event of late/nonpayment, and helps to weed out bad clients.
In accordance with the Freelance Isn’t Free Act, the hiring party is required to provide you with a written contract for any job $800 and over. For jobs less than $800, or if the hiring party does not provide you with one, you can submit your own.
Below are a few sample contracts. Please note that these are examples and can be modified to suit your particular needs.
The Freelancers Union also offers a free contract creator.