The real trick is not to worry about all the work, the exams and being a student.
Your first few weeks should just be about enjoying yourself and adapting to a new environment. It was how I was and it helped me greatly.
As for cliques: None at all. I know every single person in all my chemistry classes quite well. Though we didn't have cliques at my high school either :).

Okay, I'm off to university in September, so I also have a question for all of you post-secondary veterans.

How much extra stuff is too much?

I'm looking at what I can do in Saskatoon, and as it stands right now I want to play in a box lacrosse league, a field lacrosse league, join a martial club, and play intramural ball hockey. Most of these don't overlap, so there aren't any ridiculous days, but...even if you've spread it out, is it that too much extra stuff?

It all depends on your schedule. If you have to take night classes (which really aren't that bad at all) then you might have to do less. But I've noticed that if you have every night of the week filled up you end up wasting a lot of your time waiting for things instead of doing work, which is bad, and you'll get really drained and burn out quick. It's good to have one or two night free during the week to hang out with friends or to catch up on work if you need to. It gives you some good time to really get some work done. That's just me though.

I currently work at my job Mon, Thurs, Fri nights and Sun days, leaving Sat ngiht for going out, Tuesday for crazy club stuff and going to pub quiz and leaves Wed and Sun night for catching up things.
Having two free nights in the middle of the week is really useful sometimes.

I think it depends on the person and their specific work load/study habits as well as the specific group's flexibility and schedual. I was in fencing club, which met three nights a week for two hours, and the Swing Society (swing dancing club), which met for one night a week for two hours (as well as going to the Fountain Square dances), and it was okay for awhile, but as I got farther in the year, I found going to every practice was getting very difficult as well as juggling the nightly homework (especially the days where I had lots of classes back to back). But I'm the type of person who likes to allot a lot of time to studying and then relaxing or drawing, so when my schedual gets all crowded, I get anxious. Some people did way more than I did, and did fine, just because they're that type of person.

So it's just whatever works for you. I say go out and try it all, and if it gets to be too much, drop something.

One thing I suggest you do is to keep up to date with any course info and changes. If you have an email account your university/college will be using to contact you, check it daily, posibly a couple of times a day if you expect new information.
Some lecturers will email their class if they are going to be late or if the class has moved so it is useful to find if any changes haave been made. (One examle of this is when the roof leaked and closed off the entire floor of the uni I'm at, some classes cancelled, some shifted, only way to find out was checking e-mail as the notice board was up on the 5th floor.) Deadline updates are good to keep track of, just in case. Not sure if all of them do this though.

One of my friends suggested that I should try to take a difficult class or two during the summer because they tend to be easier then. Anyone else have experience in trying this?

Summer Classes are great. take your gen-eds and other requisite classes that you don't have much intrest in over the summer. shorter semesters, mostly apathetic teachers, and the best part: they're cheap! if you're actualy interested in the subject matter/really dig the teacher's style, take the class during a regular semester.

College, at least from my very jaded perspective, is life on training wheels. you've just spent a good portion of your life sitting in a classroom being told what to do, what to memorize, and your parents were always there to help out. now you've got to figure out how to learn, how to think, and how to deal with other people and thier bullshit.

its fun! its difficult! and if you fuck up? no harm done, its just college. stay in the dorms for a year, find out how awful they are. have some roommates, find out how terrible they can be/how terrible you can be. hang out with people from your major (don't declare right away, by the way), hang out with people in other majors.

learn to cook. i wish i had done so earlier. i almost killed myslef on microwaved food my first year. its cheaper, healthier and tastier than oven pizzas and mac&cheese and ramen.

oh, also, i dono what your long-term plan is, but don't expect to graduate in four years. colleges make it excedingly difficult for people to do this anymore, and even my friends (who were much better students than I) still took at least five years to finish thier degrees.

If you're buying drugs from somebody you don't know, confirm beforehand that they are, in fact, drugs.

It cost me forty dollars to learn that lesson, but I'm giving it to you guys for free.

I'd advise on trying to get one full credit each summer, if you can. That way, you can have more time to relax during the full year, since you have a credit out of the way and you won't have to do as much work.