Go to a place where you're likely to find other gay men.
When an attractive guy passes by you, attempt to make eye contact.
If you make eye contact, don't stop. Walk three more steps.
Turn and look over your shoulder. If he's interested, he'll do the same.
Face forward a walk three more steps.
Turn and look again. If he's looking at you too -- bingo!
Go up and introduce yourself.
Repeat as necessary.
This technique can also be used in shopping malls, airports, or anywhere there are large numbers of people and room to walk.