How do you not allow other people to enter your room?

Well, there are several things you can do. You can tell people that you don't want them in there. You can buy a doorknob with a key lock and make sure you are the only one with a key. You can put bars on the window and implement other security measures. I think another thing to think about is *why* you don't want anyone in there. Maybe it is a good reason... but restricting other people from your space also creates distance and sometimes alienation.