I bartend on occassion here's what I've learned.
Don't get'em to stinko or they won't remember you.
Girls asking for blended drinks are 9 times out of 10 flakey. If they want a White Zifindael, then they think the have class but are absolutely clueless about it. If the want a wine, they are high class, a bit more prudish. If they want a beer, then they are down to earth and cool. If they take straight shots they are sluts.
"The Rule of Four." I did this for fun one night, I gave some girls a couple of shooters that only had mixers and no alcohol. After taking four of them they claimed to be hammered and started acting slutty. In reality girls just use booze as an excuse to be what they truely are.
Watch for the girl that has a gaggle of guys around her and doesn't seem to be buying her own drinks. She is a manipulator.
As a bartender if you notice a guy who is digging on the same girl as you. Give him some free shots and booze, that way he will be way to drunk to be smooth. Makes it easier on you.
You'll have two types of people come into the bar. Regulars and one-nighters. One-nighters just show up out of the blue for many reasons: just passing through, bad day, bar hoping, trolling for skanks. Go after the one-nighters first, since they won't be back they won't burn when talking to the regular clientel. Only pursue regulars one at a time and over long periods of time so no one figures out your just there for the sex.
Most of all you're going to learn most of this on your own, just keep your eyes and ears open and you'll learn it quickly.
-Grey Fox