The 'LSE-101' Curriculum:
Pool Etiquette Overview
General Awareness
Entering the Pool
Passing & Being Passed
Common Sense

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My other projects: 
Financing the swim habit
Endurance fun on land

Other Resources:
Bill Haverland's incredible Swimmers Guide Online - the most comprehensive listing of lap-friendly swimming pools all over the world.

Swimmers should observe and respect the pace and workout routines of other swimmers in their lane - especially when circle swimming - avoiding actions that are likely to interfere with those routines.  Examples include:

1)      Slower swimmers starting a set should wait to push off the wall until faster swimmers have passed (i.e. don’t push off right in front of a faster swimmer who’s coming into the wall about to turn, as this blocks the faster swimmer).  Slower swimmers should push off almost immediately behind a faster individual or group, thus extending the time until they are lapped again and need to stop.

2)   Faster swimmers starting a set should give slower swimmers as much “running room” as possible before pushing off, (rather than jumping right behind and immediately tapping their toes to move over.)

3)   Allow swimmers doing faster strokes to go ahead.  For example, those swimmers doing breaststroke, stroke drills, or a using a kickboard should stay aware of the likely need to give way to swimmers doing freestyle - usually a faster stroke.

4)   Try to select or negotiate workout routines complementary to others in the lane.  For example, a set of short backstroke sprints may be difficult to weave in with others who are already doing a long, steady freestyle set without interfering with each other.

5)   Swimmers resting or otherwise waiting at the wall should stay far to one side of the lane, (preferably at the left from the perspective of an approaching swimmer, or the right from their own perspective looking back up the pool).  Resting swimmers should specifically avoid standing or floating in the middle of the lane as this interferes with swimmers  "swimming through" who need to tag or flip at the wall.  If the lane is crowded, other swimmers may need to rest out away from the wall along either side of the lane.

6)   When circle swimming, swimmers should never stop in the middle of a length (e.g., to adjust goggles), as this may cause a trailing swimmer to run into them.  Unless one is swimming in 'split' format or alone, it's best to continue to the wall and stop there.  If the loss of a contact lens is at stake, it's easy enough to close one or both eyes for a few strokes and swim by 'feel' to the wall.

If the pool is busy (i.e., three or more people in most lanes), those swimming in lanes by themselves or with one other person may want to continue circle swimming even after a third swimmer leaves their lane (since others will likely join the lane again soon, requiring a switch back to circle swimming anyway.)

A swimmer entering an open lane, or joining one person in a lane that's designated differently from their expected pace (i.e. a faster swimmer in a “Slow” lane, or slower swimmer in a “Fast” lane), should stay aware of arriving swimmers, and be prepared to move to a more appropriate lane if/when other swimmers join them.   That is, the lane speed designation takes precedence over the pace of incumbent swimmers who simply happen to be swimming there.

Some pools have special rules about what is and is not permitted in lap lanes, including pools that require circle swimming, even if lanes have only one swimmer each , and other pools that expressly forbid circle swimming, regardless of what swimmers in a lane might agree amongst themselves (confused yet?)   Some pools place restrictions on strokes other than crawl.  

If it's not obvious, ask a guard about local rules and/or about the best place to do laps.  Some pools will even add another lane line if a swimmer requests it and the play areas aren't particularly crowded.  Alerting the guard(s) that you're a "serious" swimmer may prompt some extra vigilance on his/her part in maintaining the integrity of lap lanes versus 'play' areas.