Have fun man.
Your first year can be scary, especially if you don't know anyone at the school. My advice is to just be social and friendly the first week or two of school when everyone's new and looking to make friends. It's not unusual at my school for someone to leave their door open and for people to just walk in and introduce myself. My point being that you shouldn't worry about not knowing anyone because everyone else is in the same boat.
Going out and drinking can be fun, even if you don't get hammered. As long as you don't do it a lot it shouldn't affect your grades and possibly get you laid.