I'm a sophomore in college.
I agree with the belief that you should work during the day and relax and/or party at night, but this is far easier said than done.
All schools, no matter WHERE you go, will have some ridiculously easy classes and some that very time demanding. Ratemyprofessor.com is a fairly good way to learn what you can expect from certain professors when picking classes, but remember: some students do poorly in class because of their own wrongdoings and then they write negative comments about the instructor.
I am a bio major, and I have gotten by with all A's and B's without much effort, but I am lucky, trust me, I have been lucky. I would still have a GPA above a 3.0 if I were to have gotten one or two C+'s instead of B-'s and so on as it goes higher and higher, but I have had some professors that bumped my grade up a little bit. Studying two hours a day would be great. In reality, three hours of studying would be ideal, but two hours everyday will likely land you with all A's if you commit to your schooling, but part of that just comes down to how well you understand things right off the bat.
No one can really explain what college is like because everyone has a different experience. To be honest, from my perspective, I would say give up on some extracurriculars to save your social life if things become too hectic. You can still do these things on your own time, you'll just be able to CHOOSE you do them. NOTE: this is assuming that when you talk about extracurriculars you meant being part of a team or club.
I love my social time, and even though I have a 3.5 GPA which I am proud of because I know some of my classe were/are rather tough, I am realizing more and more that devoting time to school will pay off a LOT in the near AND distant future, Don't get me wrong, on Friday, Saturday, and some Thursdays/Sundays I do no homework at all. It's not that hard to balance work and play, you just have to commit to making the right time for both of them.
In the end, remember: Have Fun! College can be unlike anything else! Don't stress out too hard but don't make a joke of it! It sounds like a very common sense idea, but never forget to have balance, and if you maintain balance, you will succeed.
Learn from mistakes. If you don't do so well on an assignment or an entire class, own up to it! Don't blame the instructor if it wasn't really their fault! Tell yourself you won't make that mistake again.
To close this out, never forget that college life, both academically and socially, can be applied to this statement: It's a marathon, not a sprint. You have four years of it (most likely). Don't study so hard that you feel like you're totally losing your social life and your sanity! But don't party so hard that you have to leave college after a year or two.
Hope this helped! From one college student to another (future) college student, feel free to ask me anything, because I know what it's like to be in your shoes.