When approaching, while it is situational, I prefer to keep a mildly subversive vibe, bit of a raised eyebrow, a slight smile (examples below), like I know something she doesn't or a bit more conspiratorially, like we both know something others present do not.
If you get this, this, this or this, then congratulations, my friend, you just boarded the Express Train to Poundtown, and things are looking good.
In terms of "openers", I just everything from "Hey, there" to "hi, kitten" (In Russian, with Slavic girls; it works in Russian, but would sound odd in English), to "Well, hello there....Little Red Riding Hood....", which, while that may also sound odd out of context, works a much higher percentage of the time than you would think, because it is a subtle declaration of your intent (i.e. that you are going to seduce her) thus differentiating yourself from all of the "Nice Guys" who are trying to "nice" her into bed.1 Basically, if the girl likes you, you can open with anything, except maybe this.2
The point is, you younguns should be out approaching, going over the game films and working on your skills until you aren't younguns anymore, you're Young Guns.
Now go forth and SLAY!
1 Q: How many "nice guys" does it take to screw in a light bulb? A: Two, but they don't screw in the light bulb, they just compliment it and then get mad when it won't screw.
2 For folks who like to hate-read my posts: Obv Hitler was a Bad, Bad Man. Do I have to tell you that?