I'm going to pharmacy school in kind of a weird program so I never actually lived in a dorm, but have lived in a house with two other girls for a few years now. These are things I've learned from friends in a dorm:
1) You'll need lots of the same stuff no matter where you live (sheets, towels, clothes, alarm clock, etc). Think back to a standard day of high school and remember what you used on a daily basis. Take all of that!
2) Most dorms give you the same furniture (2 beds, 2, desks, 2 dressers/chairs). Sit down with your roommate and draw out sample arrangements of how you want your stuff to be in your room (or do it in photoshop or excel and email it back and forth if you don't know your roommate). During this time, read your housing rules and see if you can save space by raising or lofting your beds. Having a plan will help save you (and your parents) lots of time/frustration during move-in day. Depending on how much you want to move the furniture, those plastic slider things might be helpful.
3)Also with your roommate make a list of the big things you will need (fridge, microwave, coffee maker, TV/wall-mount, rug, etc). Then for like a week ask family members if they have any of those things that they would give or sell to you. If you know anyone moving they might be getting rid of the things you need! Also if you know anyone moving ask for their boxes when they're done. After that, go back to the list of what you still need and try to split the costs as evenly as possible.
4) You are going to college to get an education. Yes it is an extremely fun time and I've loved every second of it, but school is still the whole reason for going. Keeping an organized calendar is essential. Hang one on the wall to share with the roomie so you know when her tests are because she will likely be waking you up when she comes in from the library at 2 AM. Keep one for yourself in your bag so you always have it with you. You will constantly be scheduling meetings with professors, club events, study sessions, and coffee dates with friends. I seriously cannot stress the importance of a planner (PB teen and Lilly Pulitzer make adorable ones). Also remember school supplies (binders, pens, note cards, staplers, post-its, etc). Having a small book light will likely come in handy during those late-night study sessions.
5)Random things no one tells you about that you will likely need: extension cords and surge protectors (there are never enough outlets when all the girls on your floor are crammed into one room getting ready to go out), ethernet cord (ask someone who has previously lived in your building about the wifi strength. I've found most buildings say they have wifi but the signal is really weak because of the concrete walls), 3M strips to hang things on the wall, a fan and extra blanket because you'll likely be uncomfortable with where the thermostat is set, rubbermaid container things for storage, basic cleaning supplies (I love the clorox wipes for little spills), Fabreeze, Tide-to-go pen, small tool-kit, etc. There are so many little random things we take for granted since our parents have always had them. Luckily if you are in a bind and need something, walmart is usually just a few minutes away!
6) Do your research before you make a purchase. Target, Walmart, and Bed Bath & Beyond will become your favorite stores. BB&B always has coupons and they accept them even if expired. You can save so much money by using them! PotteryBarn Teen has darling dorm stuff every summer so check out their website.
Ok sorry for the novel, but this will be one of the most exciting times in your life! Let me know if you have any more questions!