Alternatively, I suppose, draw your husbando(s) in tight swimwear...but I digress.
The primary focus here will be on anatomy and realistic posing. Since swimwear is so revealing, there's no place to hide where you might be having some trouble with proportions. After I finish catching up on my anime, I will post an example to the best of my artistic ability.
Rules...or rough guidelines, if you will...
>Must be a full body shot. At least one hand should be visible, although the other can be obscured. This is an anatomy practice, after all, so I would recommend showing what you can.
>Swimwear should cover what would be censored on daylight prime-time television...although realistically speaking sometimes the nips to show through.
That said, have fun and make your obligatory ecchi beach episode dreams come true.