(Based on what I observed while waiting for the elevator at a friend's apartment building.)

  1. Wait until late at night. At 9pm, your neighbors may wish to use the elevator. They will assemble into an impatient mob near the elevator door.
  2. If you have stopped the elevator for your activities, don't start it again until you are fully clothed.
  3. If you have disregarded the previous suggestions because you are an exhibitionist and want others to catch you, may I suggest that instead you have sex in the stairwell? Even more thrilling risk of discovery, with less inconvenience for your elevator-using neighbors.