Many graphic designers and photographers, when working with clients, prepare a contract to lay out the specifics of their agreement. If you are starting a business, you will certainly want to have details laid out so both parties know what each is responsible for.
What is the exact cost of the project? Is there a payment plan (ex: 50% now, 50% at completion of the assignment)? What final product is the artist providing to the client (ex: both color and black+white versions of the finished logo, each version in a .psd file and a .jpg file)?
This article on Mule gives suggestions for preparing a contract and working with clients.
You may also want to search ‘photography contract’ (or your chosen field) online to find sample contracts to work from.