Not like I'm a big expert or anything, but in addition t trimming well or shaving, I think taking a bath before you go (then of course taking a shower at the incall, as usual) would be best, IMHO.
I actually give myself an enema. I do three flushes. I doubt the lady who rims me cares that I go to this length of cleanliness. I recall reading an old post where a provider named Shun Shun even spat out a kernal of corn while she was rimming a client.