Besides what is above:
Use quick connect spades for wire ends... makes removal for bulb changes or anything else very convienent.
Also use a relay so you don't steal power from existing circuit and may cause a blown fuse in it.
Don't touch xenons... never touch....
if you have the cold weather package, put the rings on, then turn the car lights on to have the self leveling lights move so you can adjust to make sure the rings don't interfere with their movement.
hmmm.. not much esle i can think off....