The most important thing is time management. There is a lot to do, and not enough time to do it (my biggest problem is always that I don't have time to do everything I want to do, which is a great problem to have). It's important to set your priorities, and make time for them (priorities may include staying in shape, getting good enough grades, making time to hang out...). When you set your priorities, it's important make them realistic, and know that there's always a trade off and opportunity cost to your time. So say you want to get straight A's, know that it'll require a lot of time, and thus you'll have less time for other things (you can get straight A's and still do other things, I'm just saying you can do less of other things). For example, you can't get straight A's, be a member of 3 clubs, volunteer in 2 labs and a hospital, play video games, and follow 3 tv shows. In addition to setting realistic goals, it's important to use your time efficiently and not procrastinate.
Another important thing is to figure out the best way to learn in a class. Every class and professor is different, and you should keep an open mind and try out a few methods of note taking, studying etc., decide on what works best, and use that. For example, different ways of note taking may include pen and paper, printing out lecture slides and writing on them, and using your laptop. There are also many ways to study, including reading over lecture notes to identify what you are shaky on, and then going over that, reading the textbook, making review sheets, doing practice problems, watching khanacademy.com or youtube videos, going to office hours, using free tutoring services, studying with friends. Again, your time is limited and you can't do this all, so figure out what works best for each class, and use it.
Socially, I'd recommend (especially in the beginning) being friendly and introducing yourself to people. Everyone is in the same shoes and is looking to make friends, and lots of people will go introduce themselves to random people(so it's definitely not weird to approach strangers to introduce yourself). I'd especially recommend doing this to people you'll likely see a lot, such as kids on your floor, in your classes, who you meet doing something you like (ex. playing basketball) etc. You can always meet new people and make new friends, but the beginning of freshman year is the best time to do so.
Edit: Keep your door open too, especially in the beginning. Its a great way to meet people and make friends.