Usually you can collaborate a bit. Tell them if you have a bad bruise somewhere. Tell them if you don’t want your face in the shot. Prepare them, for instance, if you’re a squirter. Let them know they are going to get soaked.
Communicate honestly and respectfully. If you have an idea, most camera operators are open to trying something you suggest (themes, angles, etc).
Sometimes photographers are willing to trade the shoot for the photos. They will use the photos in their portfolios online or in print. In return, you get a free photo shoot to update your promo. This is called Time for Prints (TFP).