My Sony slave takes all the pics for me
As dingo said, you have to deal with the car's location, if it's parked in the middle of nowhere it's much easier than stuck between 2 other cars
I often crouch down when it's possible, but it's really painful when you have to do that a few times (sometimes I almost fall down
)
Being a bit tall and not having a directional screen on my digicam it's impossible for me to take some "down lows" so I just stand up and shoot down (I call this the lazy-mode)
Tripod is only for shitty light conditions, I always bring my pocket tripod with me and the "big" tripod when I know it'll be useful (dealerships, museums or so)
The golden rule is indeed
"put the whole car in the damn pic, if you can't, don't shoot or try something else"