If I can't see, I take the lane. Parked cars, corners, hills. Same if I can see, but I know from experience that seeing anything from a car on that stretch is difficult. (There's a hill in my neighborhood like this.)

+1 on what everyone else said about line of sight and speed.

On descents, I scoot way back. Not quite as far as lph, but as far back on the saddle as I can get. I'm trying to avoid the death grip, but that's easier said than done.