Going along with the cold weather thing, prepare for rain too. It will POUR. Bring rainboots, an umbrella, and a rain jacket. You don't want to let it cut into your time. And rainy days are prime for playing in the parks.
Network - Whether this means attending a meeting put on by the CP specifically FOR networking, or simply establishing and maintaining good relationships with your managers. I am still really close to my superiors, and not only did it make my job a lot easier, but hopefully it will benefit me in the near future, trying to go back this Fall.
Make lots of friends - This may sound dumb of me to say, but really what I mean is... be open. Don't hold yourself back or sit in your room all the time. Develop relationships with your fellow Cast Members - my best friends were my coworkers. Once again, not only does this give you a social life, but it makes working much more pleasurable. Just remember, almost everyone is in the same position: A new environment, doing new things, where they don't know ANYONE. It's so much easier when we're all in the same boat.
Take advantage of all the CP has to offer. Reinhart went over this already. But aside from just Housing events and stuff, I think part of the reason my program was so great was because I was ALWAYS busy. I always found something to do and someone to do it with me. If I wasn't playing in the parks, I was using my CM dining discount at one of the expensive restaurants (the holiday pack mentioned gives you 30, 40, and 50% off). Just always remember, you are LIVING in Disney World. If you ever need a reality check, just come to these boards and see how far in advance families go to plan just a one-WEEK vacation... and you're there for a SEMESTER. Crazy.
Be financially wise - Don't hold back from doing things that are awesome. Eat out on Disney property a LOT. But if you really want to make money, just watch what you spend it on. Disney says most people break even, but that's only because they don't save up at all, and go ahead and just spend their money paycheck to paycheck. However, my roommate was trying to save up for her apartment when she got home, and she came back with $6,000. She was only there August-December. So even though you'll be making minimum wage, you can REALLY make bank too, if you try even a little bit.
If you're under 21, just don't risk it with alcohol. One of my close friends extended his program through Spring and just got terminated a few weeks ago for this. It's the #1 reason for CP termination, so be very careful.
Security can be pretty hardcore - just in advance, let me tell you to never hang a towel out to dry over your balcony. Never put a pair of shoes outside to dry. Never leave your door cracked open if you're just running out to the car for a second. They will GET you. haha. I guess it's to prevent liability for what could get stolen. So, just to avoid getting yourself a warning, or 2, like we did - go ahead and steer clear from doing those things.
Go on the Hub on a regular basis... make it a daily activity. There are so many cool thngs on there and opportunities to sign up for CM-only tours. But they fill up REALLY fast. Behind-the-scenes of rides like Haunted Mansion, Tower of Terror, and Great Movie Ride went on while I was there. But I didn't even hear about them until they were full, so I'd make it a point to check frequently if that sounds like something that might interest you.
Go to Epcot at least two or three times during the Food and Wine Festival. Waste some money here. It's worth it. Falafel from Morocco and Souvlaki from Greece = delicious. And if you ARE 21 or over, have at it!
If you don't work at Magic Kingdom, it's worth it to pay for a discount ticket to one of the Mickey's Not-So-Scary Halloween Parties. I was a Custodian there, so I literally was able to experience every single aspect of the party without ever coming as a guest. But if you're not able to do that, it would be worth it. You get a crazy amount of candy. I loved the "dance parties" at Ariel's Grotto in Fantasyland and the old Stitch Stage in Tomorrowland - always hit those up on the job and oftentimes got Great Service Fanatic cards for it! The Boo to You Parade is my FAVORITE of all time as well, and Hallowishes is also something exciting to see. Loved it.
And lastly for now, if you're a Disney freak like me and think there are SO many things you are going to want to do, make a list - My next CP, whenever that may be, I fully intend on making a list of things I want to do that I didn't do last year. It sounds a little awkward, but I think it will be a lot of help. Even random things like, "Step foot inside every Disney resort at least once, just to see what it looks like in person," or "Go see Cirque du Soleil." You'd be surprised how hectic your life will get once you finish training and start working.
You guys and your Magic Kingdom! Epcot needs to get in on this face-painting business!!! 
Disney withdrawl...must...go...back...
