Re: Hammering out expectations with the roommate, it's something you have to do, and you're smart to want to do it sooner rather than later, but try to be diplomatic in your phrasing. One of the most useful things I learned in psych classes is that persuasion depends almost entirely on how something is put. If you sound didactic and absolutist, you're going to meet with rebellion (since it's a *new* roommate, it will probably be passive-aggressive rebellion, which is even worse!) If you sound diplomatic and reasonable, without compromising what you want, then you'll have a better chance of success.
For example: "Don't bring too many guests over, okay?" or "I really don't want more than three people at a time in the room," while very clear and direct, are going to result in your roommate thinking, "who are you, my mother?" and/or "hey, it's my room too, so deal with it."
On the other hand, you could say, "I like my personal space; could we make a rule that neither of us parties *in* the room?" or, "I like to go to bed early/study late, so I really need things calm around here after 9pm - is there something I can do for you to even out that kind of compromise?" These are, of course, much more indirect ways of phrasing what you want, but they achieve the same goal (no heavy traffic in the room) and they make it clear that you're sympathetic to the fact that she has her own needs, and that you're willing to give a little to get a little.
Both a dresser and under the bed storage are good options - though watch out if you have to share a dresser. In my room, we had one small dresser and one wardrobe cabinet with some shelving... my roommate took the dresser and I took the wardrobe, which had a little less storage space but was padlockable. Once I had a roommate I trusted, I took the padlock off.
I brought home bags and bags and bags of clothes, to be honest! I'm not a clotheshorse by any means, but I figured having more clothes would mean I could do laundry less often (the laundry facilities were expensive, ancient, painfully slow, and crap). That turned out to be a bad plan, because it made me desperate for space and I never wore most of what I brought anyway. In the end, I kept about a week's worth of interchangeable "outfits" (jeans, slacks, t-shirts), one set of really nice clothes for any formalish occasions, two pairs of shorts, two sets of sweats, one sweater, one light jacket, one coat, one pair of shoes and one pair of boots (I would've kept one pair of sandals/flip-flops if I shared a bathroom, but I didn't, so those weren't necessary. If you will be sharing a bathroom, you're going to need a pair of those, too, unless you want athlete's foot!) That was more than enough.
I also culled my sentimental stuff *way* down... pictures, knick-knacks, graduation gifts that were more kitch than useful, etc. It's tempting to take all that stuff with you, especially if you're going a long way from home, but it just gets in the way. As much as possible, everything you pack should have a *use*... preferably more than one use. The only real momento of high school I kept with me was a really nice, solid coffee cup that had all of our signatures on it - nostalgic and useful in one.
I got rid of all my framed photos, had copies made, took the original ones back home for safekeeping, and just taped the copies on the inside of my wardrobe - that way I could still look at them without sacrificing space or worrying something would happen to them.
A quilt my mother made for me when I was 3 went back home, just because I couldn't stand the idea of anything happening to it.
I went from having three or four stuffed animals on my bed (all sentimental ones) to one on my bed and a small Brain (as in Pinky and the, from Animaniacs... dating myself, here) perched on my computer monitor.
Books... I brought almost all my books back home, which nearly killed me, but there's very little time for pleasure reading, let alone pleasure re-reading. I think I kept about five paperbacks, just for those nights when there was nothing going on and my brain needed a break.
When I was in school, technology was nothing near what it is now (no iPods, portable HDs were outrageously expensive etc) so I had a ton of CDs... I dumped all the cases back home and slid them all into a portable folder. Same for my DVDs. As burning technology improved, I burnt copies for school and sent the originals back home for safekeeping.
I'm a board game geek, so I consolidated the pieces from several different games by dumping each game into a plastic bag and stacking them in a tub that slid under my bed (Eurogames are pretty expensive, $50-100 a pop, and they tend to go out of print within a few years, so I didn't want them lying around or big shiny colorful boxes attracting attention).
Some of this will depend on how big your room is and how much stuff your roommate brings, but count on having less space than you think you'll have... and above all, try not to bring too many things that qualify as either clutter, or irreplaceable. Don't forget you'll need space for your *new* stuff that you'll acquire as you go.
