yeh that can be tough sometimes.. im going beaching this week cuz its summer holidays here in australia and its a good place to practice but can be a bit daunting.
ok iv noticed a few things - everyone is generally in a relaxed, care-free mood when they're at the beach. u can use this to ur advantage by opening with a light-hearted comment or humor [remember always enter a set with equal or more energy, but not too much more]. i wouldnt advise using an opinion opener on the beach unless its relevant to the situation [e.g. "What do u think about guys in speedos? Hot or not?"]. better to open sets in general if they're just relaxing on the sand and talking or something [i.e. not really moving or in the water].
i would also advise against opening sets with parents unless your game is pretty tight and ur confident u can handle this situation. and if u do then remember to get their interest first and ignore ur target for the first few minutes of the interaction [u MUST win the parents over first, otherwise they will probably perceive it as a PU and be protective]. once ur in with them, then simply isolate ur target by saying: "hey u guys wanna go get some ice cream?" most probably the parents will say no to this and at the same time appreciate the fact that u invited them anyway, lowering their defences to let u run ur game on their daughters.
if ur gonna game girls in the water u should definitely start off with a joke or neg.. usually u'll find lots of girls in the shallow end yelping about the water being cold and their reluctance to go in etc. u can make up some sort of joke about this or just dive in right next to them on purpose to splash them or just outright splash them as a joke and say "oh sorry i was aiming for ur friend over there" with a smile and go from there. but of course, it all depends on ur delivery.
good luck man,
happy sarging.