If you’re a woman:

Look for a man (preferably one who is by himself) who is attempting to buy a drink. Go up to him and say “Hi”. With luck, he will buy you a drink. Otherwise, find a different man and try again.

If you’re a man:

Find a group of at least 12 people to go drinking with. Arrange it so that yours is the last round. When the time approaches, do something to be thrown out of the bar. Then, if the others want to continue drinking elsewhere, find the most inebriated member of the group and say, “Sorry guys, but I think I’d better take X home, and make sure he gets there alright.”. If the most inebriated person is you, then pretend not to hear anyone asking you to buys drinks.

The only downside to this method is that it rarely works more than once or twice. It is therefore important to find a new group as soon as possible.