1. i never roll UP the window with the door closed, although rolling down is ok. Having redone the window mechanisms, I found alot more stress on the regulator and the guides when rolling windows up especially if you've got a tightly sealing window.
2. I try to be gentle when shifting gears to lengthen the life of the shifter bushings.
3. I clean off the automatic antenna before lowering. Quite a bit of road grime sticks to a lubricated antenna that may gunk up the mechanism.
4. I check under the car for leaks prior to driving, and check the under surface of the hood after driving.
5. I am gentle with the stalk when forcing a manual cancellation of the turn signal.
6. I do not let an uninitiated passenger adjust the chrome vent louvers, they may break it (from experience).
7. I leave the windows down a bit when not driving to preserve seals.
8. I won't adjust the odometer with the car moving.
9. I won't adjust the clock backwards, only forwards.
I've got some others too embarrassingly obsessive/compulsive to mention.