Here are the rules of the pool:
Never interfere with anyone else's workout.
Pick the proper lane for you and stay in it. Most pools have lanes designated for fast, medium and slow swimmers. Ask the lifeguard for help if you can't decide where you belong.
Go with the flow. Most pool swimming is run in circles -- everyone stays on his or her right, as on a highway. The lane line is the divider. When you get to the other end of the pool, simply turn around and come back on the other side. Sometimes, if there are only two swimmers in a lane, the lifeguard will allow them to "split the lane," or go back and forth on one side. Careful here. Wait until all concerned parties know that lane-splitting is in effect.
Yield right-of-way to faster swimmers. Don't stop mid-lane, but pull out of the way when you reach the wall to allow the speedster to pass. It's considered courteous to be aware of the others in your lane so you automatically know when to pull over, rather than waiting for your foot to be tapped -- the "please let me pass" signal.
If you wish to pass someone, tap the slower person's foot (once will do). Never push off in front of someone who is coming up fast from behind and would obviously like to go ahead of you.