how do you approach two girls? what routine do you guys usually do?

You can do this in one of two ways.

1) Have a wingman accompany you. This is the best and easiest, and is more fun, if you get along with your wing. Just open the set naturally and set up a conversation that involves all four of you, then after the initial period of making the girls feel comfortable, your wing will take the girl you aren't interested so you can isolate the one that attracts you (obviously later you'll trade roles with your wing and sacrifice for him).
2) Approach alone. In this situation you have to have a stronger command of social dynamics, in the sense that you have to keep both women engaged, at least for a while, even as you communicate romantic/sexual interest ONLY to the one you want. At some point you will be able to isolate the girl you are interested in, but because girls go out in pairs and are usually loyal to their friends, you will only be able to isolate your girl later at night (or day, if it's a day set), once the other girl has begun to see you as good for her friend. Once you've been accepted by the friend and the girl you're interested has become sufficiently attracted to you, the friend will (usually) find a way to leave you two alone.

Just realize that approaching alone is quite a bit more difficult, because you have to balance the social needs of two women at once. Also, men who are alone are easily viewed as "creepier", because you're acting like a lone wolf instead of a normal guy who has friends that he goes out with.

Cheers, ~50

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--== I'm just learning this stuff too, so take everything I say with a grain of salt and follow your intuition ==--