I made out with 3 different chicks this Wednesday by using this trick:
1. You greet the girl with something like: "Hey, how you doing?"
2. Then you ask here: "So where's your boyfriend?"
3. This is the step where you cross your fingers and hope she says: "I ain't got a boyfriend"
If she said that you can proceed to step 4. But if she said something like "Over there" or "He's at some other party" you walk to another girl and redo the steps.
4. Now you gotta turn your charm on. Say something like: "Are you kidding? You're fucking hot and you ain't got a boyfriend?!"
5. Step 5 for me was to kiss her

You might need to seduce her a bit more sometimes but well. Use your brain...
Good Luck