Before beginning any job that is more than a favor for a friend, please seal the deal with a written contract outlining in detail the job description, all specs, transfer of rights and terms. It is very important to speak to your client and discuss all the details of the job including deadline and their budget so that you can devise a written contract and come up with an estimate for a fee based on their needs. Try not to settle on just a verbal agreement, they do not hold up in court when your client does not pay you. Even saved email messages are better than verbal agreements.
In the contract, note that this is a written agreement between you, the Artist and the Client. It would be wise to outline the following on your company logo, with contact information at top:
The client's contact information, name, address, tele number
Job date, Job number
Job description of kind of project (whether it is a brochure, postcard, letterhead, sign, website, etc.) with dimensions, folding, colors (4/4 or 4/0), on type of paper, amount to be printed
Job deadline and other due dates such as when all supported material will be supplied from client, sketches due, comps due, final due, print date
Fees for each project and how Payment should be made (I like either the 50% upfront, 50% when final is approved or 1/3 payments methods)
Usage and terms: to include copyright transfers, whether it's once, for a limited amount of time, North American Serial Rights, International or all rights (a buy-out, which demands a substantially higher fee from the Client for the Artist), etc.
Terms can include how original files are handled (usually given for an extra cost), how many sketches and revisions are included and the cost for any additional work, additional usage on other materials or media, any expenses related to the job (materials, travel, printing, etc), cancellation terms (usually I take 50% after sketches have been approved and 100% of fee if the project was canceled after the final design was approved no matter what the reason), how the Artist will be credited on the piece, copyright notice, determine the ownership of the designs or illustrations, release of your responsibility towards an lawsuit against your client for any undesirable business practices and arbitration should you take your Client to court if you do not get paid. The amount that you could go to court for varies with each person and situation, however, to me, it is not worth it for me to hire a lawyer for any job under $1,000.
Signatures. Have both you and your Client or representative hand sign the contract in person.
These are the most important features that your contract should be constructed with. For further information on how to set up a contract, look at the most recent Graphic Artists' Guild Pricing and Ethical Guidelines which can be purchased from the Guild or any Barnes and Noble. The PEGs will have samples and also give you rates and prices to base your own rates for many different kinds of projects. Other books are also written specifically for Graphic Designer's, Illustrators or Fine Artists by art lawyer, Tad Crawford and contain many, many sample contracts and letters of agreements that you can base your own from are available in bookstores.