TL;DR:
1. Don't hold up the line of other people ordering.
1a. Figure out in advance what your go-to bar drink is and, unless solicited to think of something new and exciting, order it.
2. Be nice to your bar tender and wait staff.
Um … yeah, that pretty much makes perfect sense. See, also: "Don't be a dick," a/k/a "Do unto others at the bar as you would have done unto yourself."
How to Order a Drink Without Looking Like a N00b
And you thought it was so easy.
I've only rarely ever seen a coat/purse hook under a bar, and mostly only in NYC. So standard east coast bias at work here.
How to act in any sort of queue:
1. Don't hold up the queue
1a. Know what you'll do when it's your turn; when it's your turn, do that.
2. Don't be a dick.
Yeah…that fits pretty much everything.
Well, I finally have one over all you people: I simply don't order drinks, so there!