I agree that groups are harder. I never cold approach a group, though there are people who do it with success. The problem with doing that is that at least one girl in the group is gonna be a cockblock, not like you, be jealous, or be a bitch. The best ones to approach are two girls who are just together as the two of them. More often than not, a duo is out to meet guys and wants each other to succeed at finding a guy. Girls who are alone often times are on their way to some destination and don't want to be stopped or feel separated from their group so they may be uncomfortable.

The key to any successful approach is to seem like you "get it." There's a lot to that, but it has to do with dressing appropriately, styling yourself appropriately, and showing some personality. As long as you do those things right, you're usually in for at least 30 seconds. During that time, make sure you don't come off as trying. Don't even try to not try. By trying, I mean wanting it to work. Thinking ahead. Thinking about your self image. Cut all that shit out. It's just you and the girl and the present moment. Look her in the eye with a relaxed arousal, say something warm and inviting. The key to good conversation is to be clear with yourself in what you're doing.