Coilover self install, what's the best way to ensure proper ride height?
 

When I put coilovers on my car, and I set the ride height, what do they actually adjust when I take it in for an alignment? Do I specifically need to ask them to corner balance it? Can they even do that? I'm pretty clueless, so any advice would help.

Alignment is just going to be camber and toe adjustments. Corner balancing is not normally done by your everyday alignment shops. You'll have to find a performance shop to do that. But if you're not going to track the car, I wouldn't bother corner balancing. Just drop the car evenly and you should be fine.

You'll also want to wait a few days after installation before you get your alignment as the suspension needs some time to settle and you may have to readjust height again.

If your coilovers came with camber plates in the front then the things they will adjust are:

Front camber plates
Front tie rods (toe)
Rear arm ecentric (toe)

There is no factory camber adjustment in the rear. Depending on how much you drop the car you will probably be out of spec for rear camber. This is corrected with rear camber arms either upper or lower. If you want a corner balance then you will need to go to a performance/racing shop that has scales. There they will adjust the preload on your coilovers to set the corner balance. Some coilovers have independent preload and height adjustment while others don't.