Changing heads

The best place for a good clear view of your self is probably not from inside your own head. I think the same thing applies to protagonists. While I know what's going on in my main character's head well enough, I don't know his appearance, his habits, or the impression he makes on other people as well as I might. I'm beginning to think that to get to know him better I'm going to have to get out of his head and write about him from another point of view. If only as an exercise.