don't be condescending or know-it-all. i've heard from women that the best way for a guy to approach them at the gym is to ask the woman for advice on doing an exercise. lots of them hate it when a guy comes up and starts correcting their form or whatever. also keep in mind that some gyms are pick-up spots, and some gyms are just places people go to exercise. if you try to pick someone up at the latter you are likely to simply annoy or get shot down. also, try to size her up before you talk to her. is she chatty or does she wear headphones and not talk to anyone? if she isn't much of a talker she probably isn't looking for a boyfriend at the gym and may simply rule you out automatically.your best bet is probably to just say hi when you see her next and, if she is at the gym often, say you've seen her around a lot and compliment her dedication. smile, be nice and thoughtful, and if she gives signs that she's not interested, back off and leave it at that. this is how you avoid being creepy gym guy.good luck!