A bartenders salary is actually quite low. And when I say low I mean minimum wage low. But then bartenders don't work for wages, they work for tips!
A successful bartender can expect to earn anywhere from $100 to $400 and above a night. Much of it depends upon the location and the shift you work. Obviously you're going to earn a lot less working at a dive bar as compared to a high class night club. You'll also make a lot more money working a Saturday night shift then you will on a Monday morning.
If you're just starting out you'll have to settle for whatever you can get. Don't be picky, just try to get your foot in the door somewhere. Experience is key and once you have it, you can parlay that experience into a better location and better tips. Once you've been with a place for awhile and have gained some seniority, then you'll receive better shifts.
Even if you're stuck during a lousy shift at a low class joint, you can improve your tips by being outgoing and friendly. Strike up conversations with your customers. Try to learn what works and what doesn't. If your customers like you, then you'll earn more tips. You'd think that last tip would be common sense, but you'd be surprised at the attitudes some people have who work for tips.
Regardless of where you work, keep a positive attitude and enjoy yourself. Here's some further reading on bartending etiquette if you're interested.