This works especially well on the Gulch. When Multiple enemies are at a base,
park a tank or warthog over the corresponding teleporter that's in the middle of
the map. This keeps all of the enemies herded in one area. If you're carrying a
sniper rifle with you, it's like shooting fish in a barrel.
Place your ghost over any of the one way teleport destinations (as in the center
of Blood Gulch), and STAY IN THE VEHICLE. The teleporter will not be blocked,
but when someone comes through they will be instantly killed.
This is very useful in a CTF game, as if the flag carrier teleports, they die,
and if they choose to run, you are right there to get them.
WARNING: On Blood Gulch, you are VERY vulnerable to snipers. ]