There's usually a queu, often demarcated, where you stand there and wait for the bartender to look at you and ask you what you want. If there's no visible queu, just wedge yourself between two skinny people and lean against the bar while training your eyes on the bartender. They'll eventually look back at you.

Always tip. For mixed drinks, about a buck. If it's straight or on the rocks and you have several in a row, slap down a couple bucks when you're done... position it so everyone knows it's a tip so someone won't grab it.

If the bar has (a) cocktail waitress(es), all you gotta do is sit down at a table or, barring that, stand around and look bored and anxious, and one will hit you up before long. I like those bars better because I'm lazy and don't like getting up or waiting in line...

...and because in Las Vegas, the prettiest girl at your old high school would have one hell of a long line to stand in if she wanted to be a cocktail waitress at a bar/club on or near the Strip... and that's after she got her implants done. Off the Strip where us locals dwell, and excluding lowdown redneck dives (there's plenty of those, too), she'd be good to go lookswise but would have to get visible tattoos, lip rings, and would still need implants.

Gotta love this town! :D

Did I also mention many bars are open 24/7, there's absolutely positively no such thing as "last call" unless the bar isn't open 24/7, you can drink legally on the streets, and some places will give you cocktails in to go cups?

They call it "Sin City" for good reason.