If there's anything unusual about your routine, let your hostess know as soon as possible, preferably before your arrival in case she feels she needs to make special provisions for you.
You may well be wondering what exactly a special need is, in which case I suggest you think through your own routine and compare it with those of your closest friends and family members. Is there anything that's particularly different?
Obviously, the need to take medication at specific times is a special need although not one you'd necessarily have to mention to your hostess. However, if you're on a special diet, either due to a medical condition or your choice of lifestyle, your hostess should have been informed beforehand so that she has the chance to plan meals accordingly.
Maybe you have a medical condition that causes you to feel the cold more than others do, meaning that you'll need to heat the bedroom on days when most people perhaps wouldn't bother. Maybe you need access to the bathroom at night or are allergic to cat's hair. Show respect for your host family by informing the hostess and giving her the chance to adjust the family's routines to fit in with your special needs.
Don't Clutter the House
There's nothing worse than having house guests who fill every available space with their personal belongings.
Respect that you are not in your own home even if you're told to "make yourself at home" and regardless of whether you leave magazines on the coffee table, cups in the sink or your purse on the hall dresser at home, don't do it in somebody else's home. Not even if they do it themselves!
If you've been given a room, use that to keep your belongings in. If not, use your suitcase or overnight bag. If you managed to fit your things in it to travel, you can fit them in during your stay, too.