Get a model release for all the work that you do.
A release is a legally binding contract between you and the photographer. A release will indicate in legal terms such things as how much a model will be paid, where photographs may be used and under what limitations.
It is extremely important that you read all releases (contracts) carefully. And if there is something you don’t understand, get it clarified. It is best to see all released ahead of shooting. This way you are not surprised by anything you may encounter.
Whether you are doing TFP or shooting for pay, establish exact terms of compensation prior to shooting and get it in writing. Terms may include the reception of CDs & prints to exactly dollar amount.
It is important to do this prior to shooting, so that avoid any “confusion” after a shoot when a photographer tells you, “I meant $50 for the whole shoot, not $50 an hour”. Sometimes situations like this are the result of genuine miscommunication. However, there may be other times where they are not. If doing TFP, it assures you that the photographer is legally bound to provide you with the contents of the shoot and within a specific time frame.
Establish your limitations prior to shooting (especially if you are doing any kind of nude work). Getting a photographer to agree to and sign a document stating how the photos from your shoot may be used will protect you from possible conflicts of interest. Also, discussing these limitations, and getting a signed agreement before-hand, should help constrain a photoshoot to these terms during shooting.
When doing a paid shoot, do not sign a release until you are paid.