If possible, place a note on the door before you hang yourself explaining what you've done and telling people to call the police instead of opening it.
To slow the decomposition of your body, you should make sure that your room doesn't have any insects in it if it can be helped, and you should also put an air conditioner on blast at a low temperature, if it's possible for you to do so. The lower the temperature and the less humidity in the room, the better.
When you die, all of the muscles in your body will relax and you will shit and piss yourself. Don't wear any clothes that you don't want soiled. Ideally, put on a diaper to contain all of the mess and prevent the bad smell, and get one of those air scent freshener machines.
The experience will be traumatizing for them regardless, and there is only so much you can do.