Ask the hostess what she prefers, but absent that, at least MAKE the bed. If it is a hi-riser, take off the bedding, fold it neatly, and put the bed back together if you know how to do it. The idea is to be less of a tircha on the hosts, as well as to show hakoras hatov.
I had boys sleep over by me for a school Shabbaton (their rebbie who knew my husband asked us to put three boys up). Not only did they make an unbelievable mess both in their room and in my adjacent den, they invited at least five friends to come back to my house and made an unholy racket, jumping off our furniture while we were trying to sleep. I came down to see what the noise was and was shocked at what I saw. They were NOT supposed to be in our house at that time of day at ALL. These were bar-mitzvah age boys, btw. I couldn't even say anything, because one of the boys is related through marriage to a close relative of mine, and it would be very awkward to tell them about his behavior. But I will think twice and three times before ever allowing such a sleepover again.