A service agreement, such as when hiring a graphic designer, is something you should put in writing. Written contracts make it easier to take legal recourse should the relationship go awry.
Define the services that will be performed. For example, if you are hiring a graphic designer to design a brochure, you should determine ahead of time the size of the brochure, the number of pages, the size of the text blocks, how many photos will be included and the color scheme. The graphic designer should be informed of all of the dynamics and details of the project.
Determine the timeline of the project. Designing something like a brochure, for example, requires numerous steps. For example, the designer might have to choose photos or a specific layout before going on to design the shell of the brochure. State when the designer should have each step completed and turned in to you for review. Also spell out the number of revisions that you are allowed to request and the length of time you have to review the work and provide feedback.
Clarify payment terms. This should include the overall price of the project along with a timeline of payment. There are numerous types of payment structures that you can use -- everything from one lump sum to installment payments as the work is being done. Decide the one that best fits your needs and include it on the contract.
Decide who will be responsible for expenses, if applicable. Expenses might include the cost of materials or if any travel is required to complete the project. It can be beneficial to clarify the terms for expenses even if you are not expecting any. Should an unexpected expense come up, you will already have the terms set, which can help prevent disagreements.
Settle on how any termination of agreement will be handled. You might find that you and the graphic designer don't get along, or that the designer regularly misses deadlines. If so, you want a way to legally end the agreement.