Swimwear photography is not as easy as it may sound, but it can be a lot of fun for both the photographer and the model. There are all sorts of inherent problems that must be overcome to get good results, and of course it has all been done well before!
A good starting point is consequently to consider, honestly, what is the principal objective. If the intention is to sell the images, the driving force must be satisfying the requirements of potential buyers, and hence understanding very clearly their requirements.
The first task is to find a suitable model. Make a careful and considered selection from the models available. Beach and swimsuit shoots can be messy affairs with wind, sand, waves, unwanted observers and all sorts of other hazards. A model who is relaxed, open-minded and a bit adventurous is more or less essential. A girl who lacks confidence or a good sense of fun may be unsuitable.
Make sure that the chosen model is aware of the plans for the session and that she understands what is expected of her. Ask to see the model in swimwear before the shoot - preferably before hiring her. Check that her body is evenly tanned and free of ugly tan lines, and make sure that she does not wear tight clothing that leaves marks on her skin in the hours prior to the shoot. Also ensure that any fake tan is well applied. Finally, check that she has appropriate swimwear or other clothing to suit her figure and personality, and agree the selection with her. Recommend that the model takes a full-length bathrobe to wear between sessions and agree with her some location or arrangement for changing.
Having a third person present is a good idea, particularly if they can take care of the model's hair and make-up. Even the best prepared models suffer the effects of wind and spray. If the intention is to sell images, never underestimate the value of a professional model or the need for a professional hair and makeup artist. Hiring such talent is expensive but may determine the success of the shoot. If shots are planned that require the photographer or model to be in the water, a third person can also warn of approaching waves and hold a reflector when required.
Make sure that the planned shots are executed in the best order. Once hair is wet it cannot be dried and restored very quickly. Dry shots should therefore be done before wet shots. Similarly, certain sitting or lying poses may result in marks on the models skin. Knees are particularly easily pressure marked. Sand will also get all over the model, particularly if body oil is used to achieve a sheen.
The best time to shoot a swimwear model is when the sun is relatively low over the water. Water and sky make a good backdrop, unless of course there is some very attractive element on the landward side. Backlighting works well, provides good hair light and perhaps a golden rims around the figure, and avoids squinting or strained facial expressions. Fill of some sort is necessary to reduce contrast, so take flashguns and reflectors. As the intensity of the light fades and shutter speeds reduce, use a tripod to keep the camera stable. Fitting tennis balls to the tripod feet helps to prevent them sinking too much in wet sand.
Take care of the photographic equipment. Sand and salt spray are the deadly enemies of photographic equipment and can easily cause serious damage. Take only what is required to the beach and cover equipment with plastic bags whenever possible. Some photographers use flexible lightweight underwater camera bags when working in the water.