DON’T act differently toward her in public
Whether you’re friends with benefits or a committed couple, it’s not going to last long if you get jealous when you go out, and she’s her usual friendly self with other guys in your circle of friends. If you start acting controlling or less fun, or make her less fun, then all of her friends are going to work to sabotage whatever is going on with you two. You really don’t want to be up against that.
Similarly, make sure you’re alone with her when you make your move. Find some excuse for you to pick her up (and therefore drop her off) when you all go out, or vice versa. Or if that’s not practical, ask her to come shopping with you.
DO start at the top
I fully realize that this is obnoxious, but I’m going to say it anyway. Most circles of single friends have an informal social hierarchy, and with women it’s often correlated with attractiveness. I’m generalizing here (the psychology of this gets a bit complicated).
If the woman who catches your eye is a potential soul mate, go for it no matter who she is. But if you’re attracted to a couple of different women in your social circle, go for the hottest one first. Whether you’re successful or not, when it’s over you will have a much better chance with other women in your circle than if you’d started at the bottom.