Assess The Situation
Sometimes you're doomed before you've even make your approach. We don't want you to waste your time (or take an unnecessary blow to your ego), so please, take a minute to assess the situation before flinging your body into the fire.
Does she appear to be talking emphatically with a friend, possibly giving her advice or engaged in serious conversation? Expect to approach her and receive an irritated "shoo" look in response. Does she have one eye half-open and her heels removed? If she's had her way with Jose Cuervo, she may not be the best candidate, unless tequila-scented projectile vomit is your thing (please, don't answer that).
And most importantly, if she's lingering by a particular dude, unless you're looking to tint your tan with black-and-blue accents, maybe play it safe and seek elsewhere. A quick game of Clue at the bar can save you serious stress on the battlefield. Trust.