(Based on what I observed while waiting for the elevator at a friend's apartment building.)
- 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.
- If you have stopped the elevator for your activities, don't start it again until you are fully clothed.
- 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.