Should I start with his head when bathing him and proceed on down?

If he can talk, ask him where he'd like you to start. ... I'd get the worst part over first since it gives you the heebie-jeebies and takes longer to dry. Then the legs, and upper body. Use a hair blower to speed up the drying (my pitbulls loved it), talcum powder, and a touch of cologne. He'll be grateful; and you'll be relieved.

Here are some instructions on wikihow. You need to look down a way to see where they are giving a sponge bath to someone in bed. They recommend to start from the top and work down, with the back and privates being the last things done.

wikihow/Give-a-Sponge-Bath