After you have started modeling, ask artists, photographers, and
students whose work you particularly like to let you keep one or two
of the studies they make.  Put these studies together in a large
portfolio, and bring them with you to modeling interviews.  A couple
of professional photographs should also be included, even if you do
not model for photographs.  Credit the artists.  Many artists will be
pleased to have you include their work in your portfolio.  You will
almost never find it useful to show the portfolio, but it will give
you an idea of your own progress, and will be handy in case you find
that you do have a chance to negotiate a long-term contract, or one
that offers a high rate of pay.