Yesterday somebody posted the following thread about Quora. I posted the same question to a sensible subreddit. I would say that the answers are of comparable quality.
Original link:
http://news.ycombinator.com/item?id=1439628
I would say that the following comment is at least as good
as the one provided by Quora:<p>"Here are some tips:
Most guys have problems approaching strangers and seeming creepy. If you can strike up a conversation with girls, just drop a few comments that you're hanging out with "a really cool friend". It makes things easier when you introduce him later on.<p>When you do introduce him, drop a few conversation starters where there might be common interest or where he can demonstrate expertise. If he likes cooking, mention the mean casserole he whipped up for your Christmas party or something.
Remember that this is an interaction, and you should stay until both he and the target female are comfortable in conversation. Participate in the interaction until then, and when they are warming up to each other THEN excuse yourself to get a drink, say hi to someone else or whatever.
Encourage him to lead in the interaction. The more he does this, the easier it will be for him to seem attractive. Let him choose the way the conversation is going, when it ends, etc.
It may take a bit of work to get both of you synced, but when it happens you'll be the best thing that happens to his social life."