Understand what you are getting yourself into. If you come from a family of all boys or are an only child, possibly rethink your decision to live in. You will be surrounded with girls all day and night, without much time to yourself.
Pick a roommate or roommates that you are sure you won't get sick of. Sometimes it is worse to live with your best friend, especially if you are usually with her outside of the house. Instead, choose someone who you know matches your sleeping schedule and living habits and who you don't spend every waking hour with.
Brace yourself for competition and occasional cat fights between sorority members. With that many girls living under one roof, there is bound to be at least a little drama. Invest in headphones to block out noise and ear plugs for when you sleep!
Find non-Greek friends. It is very important to have an outlet and people to hang out with when you get sick of being in the house. Make weekly gym, dinner, or frozen yogurt dates with these people to avoid getting really sick of living in.
Take advantage of the in-house chef. Usually, they provide a wide variety of healthy food 5-7 days a week. This will save you a ton of money!
Buy a lock for you door if there isn't already one. Kleptomaniacs are common in sororities, and it is easy to lose a ton of your clothes and other belongings while living in. Make sure you know who is borrowing your clothes, shoes, dvds, etc.
DO NOT disobey the house rules (ala: blatantly drinking alcohol or bringing boys in your room.) In many chapters, this will result in immediate eviction and you will be homeless.