MH does not recommend showering at all. If you have a choice of a shower or a bath, choose the bath (I don't have a bathtub in my apartment, only a shower).
Also don't use commercial soaps, shampoos etc. Rule is if you wouldn't enjoy eating it, don't put it on your skin.
Once a day seems like a good schedule. MH likes to soak in the tub for about an hour while he reads.
There is some info on the "Daily Living" page on ObeyNature.com