Say you caught your little brother rifling through your room several times when you were growing up. Now, take how you felt when he was in your room and exemplify it by 1,000. Forget about having any form of privacy and get used to being around students all the time, even ones you don't like. Secure all your personal belongings, especially laptop computers, any form of electronics and expensive items. It isn't that hard for strangers to walk down your hall, and if your room isn't locked or the door is open, into your room where your valuables are.
Yes, resident advisers will come around every couple of months to inspect your living space for safety hazards and overall cleanliness. But in between those months, it's up to you and your roommates to keep up with the cleaning. If you don't have a roommate who keeps things clean, you can have a problem on your hands. Some dormitories will have cleaning people who will clean the common area bathrooms but the rest is up to you.
If you plan on living in a dorm, forget about trying to get some peace and quiet. There could be hundreds of students living in your dormitory and each has his own version of what being quiet is. There will probably be constant noise: from music blaring down the hall in the wee hours of the morning to students constantly walking up and down the hall talking loudly. Some halls might have "quiet floors" but if you need to get some serious studying done, hike it over to the library.
Sometimes you can get lucky and move in with a roommate who is quiet, clean and on the same sleep schedule as you. However, this isn't always the case. When college freshmen move into their first dormitory, chances are they are going to get paired with someone they don't know. This person might stay up until four in the morning, eat your food out of the mini-refrigerator or invite whoever she wishes into your cohabited space. Let your roommate know if something is bothering you and if he is really a nuisance, you might be able to talk to your resident adviser about moving to another room.