Don't Single Her Out 

The fastest way to wipe out at the beach is to approach one girl while pointedly ignoring her friends. If she's there with her friends, her chief priority is enjoying their company. Plus, by singling her out, your force her to snub her friends in favor of flirting with you, which is widely accepted as a cardinal sin among women.

Rather than risk being eliminated on those terms, use a less-abrasive method of initiation by approaching the group as whole, not just your lady of interest. If you want to play volleyball with her, invite her and friends. If you want to offer her a drink, offer them all drink. If you want to address the dude you just saw lose his shorts in the surf, address the entire group.

In doing this, you accomplish three things. One, you appear friendly and fun-loving rather than being blatantly in pursuit. Secondly, you leave some ambiguity to whether or not your interested in her specifically (always more exciting!) but also open the possibility for one-on-one conversation without appearing creepy. And third, you win the advance approval of her friends, which will be necessary for things going forward.