One evening, I parked pointing downhill and like the book says, I turned my wheels to the right before parking. But I turned it a bit too far, because when I returned to the car and inserted the key into the ignition, the key wouldn't turn.

The wrong thing to do is to force the key until it breaks.

Here's the right thing to do:

Take the steering wheel and turn it left and right. One direction will have a little more play than the other. Grab the wheel with your left hand and apply pressure turning it in the direction with more play while using your right hand to turn the key in the ignition. (Or, if you're like me and can't figure it out, just wobble the wheel back and forth until the key unsticks.)

Note: I scheduled this item independently of its partner. By an amazing coincidence, both items warn against forcing something until it breaks.