Post Nuptial Agreement
Describe your obligations, including the service you must perform to fulfill your obligations under the contract and be as detailed as possible. For example, if you are writing a marketing brochure for a customer, describe the length of the brochure, the purpose of the brochure and establish that you are only responsible for providing the text, and not the layout or design, for the brochure.
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.