Pack for any kind of weather be it cold and very warm, there is little climate control in Europe.
Pack as light as you possibly can.
Read a travel book, everyone seemed to love Rick Steve's. It's great to touch base with other students going so you each may bring a different book. That creates a mini library and you have the benefit of reading different accounts as well as different cities.
Also if time permits read an 'European' theme novel; for example ROOM WITH A VIEW, A YEAR IN PROVENCE, MOON OVER PARIS, ANY HEMINGWAY SET IN EUROPE etc. The selection is astonishing.
While at bookstores looking at the travel books, invest in a couple of the laminated streetwise maps of the major cities you plan to visit they're easy to read, have the major sites and keep up in the rain.
Make sure you plan for trips while you are still here, but leave the technical logistics until you're there so you can form groups with different people. Be spontaneous.
Use the Laundromat and share the detergent with someone, the dorm one takes 4 hours. (Not unusual for Europe ) Take earplugs for studying at the foyer; sound travels really well there!
Be nice and appreciative to the cafeteria and the dorm staff.
Enjoy the food. We ate more there than ever but still most of us lost weight. You walk so much and the food is fresh and healthy. Do try new things too; usually you'll be pleasantly surprised.
Take the initiative to get to know people you did not spend time with in school prior to the trip.
Take tons of pictures. You'll be glad you did. There is an inexpensive place to buy film by the Gallerie de Lafayette.
Thank God for your adventure and realize how amazing this opportunity is for you. Before you know it, you will be back in the USA and it will be all over.