Describe the payment terms for the transaction, including the total amount for the service, how much and when the deposit is due and how much and when the final payment is due. Spell out a time line or milestones. Include specific dates for the delivery of parts of the service or the final deadline for the service to be complete.
You may want to have an attorney review and make suggestions on a template of your business contract. An attorney can pinpoint issues for your particular business that you may need to include in the agreement. You can use a business agreement template and modify it to fit your needs, rather than writing the agreement from scratch.