in discos where it is very noisy, where i cant even hear myself talk, i usually smile at the girl first from a short distance away...
once she smiles back, i will try to lift up my glass or mug to "cheers" her (you know, plus eye contacts and all that etc...). see her responses, her willingness. if so far so good, i will show her a hand sign. its a handphone sign with my thumb and last finger outstretched and raised up to my ears. it means i want her tel or hp number.
i succeeded with that on a few occasions before. but of course, getting contact number is one thing, bonking the girl is another.