You need sample shots in order to book nude models. Building credibility is an essential step to recruiting models, and nothing builds credibility better than an astounding portfolio. So how do you get your first nudes? This may seem like a catch-22, but you can get there. You may have to add progressively unclothed shots to your portfolio until you have a portfolio of nudes.
Shoot clothed models until your work is good enough to convince someone to do glamorous bikini or lingerie shots. I have rarely met an attractive woman who would not pose in lingerie. If glamour is not your style, choose a more artistic mode of half-attired subject, such as sheer drapery. Then you can move on to models who do implied nudes (nude from behind, for example) or topless shots. Sometimes you can most easily accomplish this by shooting repeatedly with the same model. With any luck at all, you will quickly meet a model who is only too eager to pose for the exact style of photography you envision.
There is a first time for everything, and I have had my fair share of models posing unclad for the first time. I do not encourage beginning photographers to work with first-time models, since neither of you will have much experience. Eventually, you will have no trouble finding your first nude model, especially if you work repeatedly with the same model or hire a model who has a lot of experience with figure work. Finding your first nude model may be intimidating, but it is not as difficult as it may appear.
Once you have created your first portfolio, complete with everything you need to impress prospective models, know this: you are not done. You are never done building your portfolio. Periodically review your portfolio and relentlessly eliminate weak or old photos. Recognize what works and stick with it or update it. Your portfolio should contain only consistently strong, recent work.
This article is from the book, True Confessions of Nude Photography