Well it depends. I'm not to awsome, but in all my sarges, both online and offline, I live by the 1 in 3 rule. Yep, thats about it.
Realistically, it makes sense... however if you send the right emails you can get a response almost insatantly 100% of the time... I've actually been working on a little online neg 'hit and run' thats becomming quite good at getting numbers fast.
Example:
Hey, I was looking over your profile on "Sites name" and I kinda thought you look like an intresting person. I mean, that 'hair stye' really speaks something to me.. whats it called, the flop?
Now the trick here is it will get you a response like 100% of the time... and often an angry one. But at least the girls getting in touch with you! lol.
But seriously, do online meetings like meetings in real life, question, comment, neg/joke and repeate. I'm no jesus at this, but I've seen a couple of my friends run it pretty successfull with high end ratios.