TFP (Time for Prints) is an arrangement between a model and a photographer where the model donates her modeling time in exchange for free pictures for his or her portfolio.
If you want to work with a model and you are not an established photographer (when you are paid good money by modelling agencies and glossy magazines for doing this sort of thing), TFP may be an alternative to paying a model to pose for you. Likewise, for a model starting up a career, TFP may be a way a way to accumulate a portfolio of high quality pictures without paying a photographer to make them.
As a photographer, you should be aware that there are lots of people who want quality pictures, but are unwilling to pay for them. Only enter into a TFP arrangement if you have a clear project in mind. As a photographer, you should be in control of the session, not the model. Otherwise you may end up exposing and post-processing a lot of pictures for free, with no benefit to you as a photographer.
When doing TFP, one should also work out beforehand who should pay for incidental expenses of the shoot (e.g. studio and equipment rent, props, stylist, make-up artist). This is not covered by the sample contract, so photographer and model need to work out the practical arrangements and who pays for what before the session starts. The standard arrangement is that the photograher pays for and procures the studio the equipment, as well as any props needed, while the model pays for the stylist and make-up artist (or bring a friend that performs these tasks for free).
Most TFP work is of fully clothed models. If the project involves nudety or “glamour” type photography, this must be discussed before the session and the informed consent from the model secured. Be aware that sexual explicit photographs of underage models is illegal in most jurisdictions, even if the photographs are not intended for publication.
I've found that for a good TFP relationship, one should always have a contract that both outlines what compensation the model can expect (e.g. how many pictures, and in what format), as well as how the photographs can be used by both model and photographer. The contract should be signed by both parties. If the model is under 18 years old, it should also be signed by the model's parent or guardian.
A fairly standard arrangement is to let the model have one or two medium sized prints for each hour of modeling time. A suitable format may be 20x30 cm, and the images should be fully post-processed and printed on high-quality photo paper. Some photograhers also let the model have a CD-ROM with digital files. But because high resolution files may be used to produce unauthorized copies, many photographers will only part with low resolution (< 1 Mpx) image files watermarked with the photographer's copyright notice on a CD-ROM.
Copyright of a photograph always remains with the author (i.e. the photographer). However, most jurisdictions impose severe limitations on what the photographer are allowed to do with someone's portrait unless you have a so-called model release form. The sample contract linked to below doubles as a (limited) model release form.
The contract and model release form is of course only a starting point that you may use for writing your own. I've tried to keep it balanced. As it is written, neighter model nor photographer can exploit the pictures commercially. You may want to change this, or to add a clause that permits commercial exloitation under some sort of profit sharing arrangement, or instead use a standard model release form without restrictions on commercial use. I've linked to a sample copy of such a form as well.