Arrive on time. If you are driving across town to get to class or just can't get out of bed, speak with the professor about switching to a later session or drop the class entirely and register again when your schedule eases up.
Leave the food and drinks at home. A cup of coffee or a bottle of water is usually acceptable, but settling into your seat with a three course meal is just plain uncouth. Keep your desk clean and it will not only give you more room to take notes, but may also help you stay focused on what's going on in the classroom.
Dress appropriately. There might not be an enforced dress code at your college, but that doesn't mean you should come to class in your pajamas. Leave the club clothes at home and opt for something that implies you are a serious student.
Put away your cell phone, pager and iPod. Nobody wants to suffer the embarrassment of having their phone's Bonanza ring tone go off in the middle of class. Many professors can (and will) throw you out of their classroom if they feel that you are being a nuisance to other students.
Stay alert no matter how hard you partied the night before. Nod your head periodically and don't be shy about raising your hand now and then to ask for clarification on something. Careful though--your professor might take note of your responsiveness so get familiar with the material since you'll probably get called on...a lot.
Speak clearly and articulately. Avoid using the word "like" repeatedly and refer to your professor by their proper name (unless requested to do otherwise). Also, if a fellow student is talking, wait until they're done speaking before butting in.
Wait until after your college class is finished to bring up any issues that would only pertain to you. Most students don't want to hear you dispute a grade or question a comment on your term paper out loud. Spare them the burden of hearing about it and catch up with your teacher later.