Increasing your tips is often much simpler than you may think.  First off, you have to remember that customers don't owe you anything.  They're leaving you a tip because you have performed your job well.  This means that sloppy bartending isn't going to bring in the big bucks.

When a customer sits down and puts their elbow in a puddle of someone else’s spilled drink, their experience hasn't started off all that well.  You, as the professional bartender, need to make sure that your bar is clean and neat.  People will enjoy themselves more if they're not constantly trying to get their shirt sleeve unstuck from your sticky bar.  Happy people tip.

When someone tips you, say "Thank You".  It seems pretty simple but a lot of bartenders overlook this fundamental courtesy.  Customers are giving you money, if you come across as rude in any way when you accept this money they, may not be as generous next time.  You'll be surprised how much your tips may be effected by a simple "Thank You".

You have to know you customer in order to serve them the best way possible.  If there is a guy sitting at the end of the bar with his date and they are talking quietly, they probably want your presence to be limited to taking their order and making them drinks. 

On the other hand, a group that is out for a birthday party may be more interested in an energetic bartender who fires out flaming shots and juggles.  Still the single guy sitting by himself may want someone to talk to. 

If you know the difference and treat each customer accordingly you will see your tips increase from every type of customer.

A simple, "Hi my name is (your name here)", makes you more personable to your customers.  You don't want to be a machine that makes drinks for them.  Obviously if you work in a high volume night club, you don't have time to introduce yourself and talk to every customer.  If you have time though, it’s a good idea.

Try to remember what people are drinking.  When you ask them if they want another one, knowing what they drink makes them feel special.  If you work in a smaller bar with a lot of repeat customers, its even better if you can remember someone’s drink the next time they come back.  Something this simple really does increase your tips and makes the patron feel much more welcome.

By doing these small things, you can easily increase your tips.  Everyone isn't going to give you a huge tip just because you remembered their drink order but if you can get a few extra bucks here and there at the end of the night it starts to add up.  Good luck.