It's not as hard as you'd think (though I won't lie, there are days when I really just don't want to work at all...) For one thing, in college you're only in class maybe 3-4 hours a day (more if you have lab, but typically that's just 1 or 2 days a week). So you have a lot more time to study. Realistically, if you're efficient about doing your work you can get it all done in the afternoon/evening and still have several hours to do whatever you want.
Here are a few things that I've found helpful
-Find a good place to study. Like you said, the library is always good. Find a couple of other places (empty classrooms, cafes) to go to just for variety.
-Start problem sets the day they're assigned. Seriously. You'll be glad you did.
-Write down all test dates/due dates somewhere (calendar, planner, whatever) so you know in advance if you have a bunch of stuff due the same day. Then, start planning/studying early so you don't need to freak out the night before.
-Never study for more than 90 mins. without a break. (I think this might vary from person to person, but as far as I'm concerned I just can't focus longer than that).
-Try to do your homework somewhere without internet. Otherwise (if you're like me) you'll just end up killing two hours online.
-Type up your notes after class; it'll help you remember them.
-If you're trying to do homework and completely unable to focus, take a break and do something else, then come back to it when you feel better.
-Try to plan something fun every day so you're motivated to do your work. If you're going to a movie at 7:30, you'll want to get your work done before then so you'll be more efficient.
-For math, chem and physics, read the chapter briefly and do ALL the practice problems (including the ones that weren't assigned.) Don't bother reviewing the chapter itself, just make sure you understand all the problems.
Most important: don't freak out. Try to enjoy yourself, don't just work. You'll get a sense for how much work you need to do, but I go to a pretty good college (top 20 LAC) and almost no one does more than 5 hours of homework a day...and there are a LOT of crazy premeds here. And never work just because "you feel like you should"...if you've done all your homework and studied for any upcoming tests, you've done enough--even if it only took you an hour. If you're done, you're done...don't create unnecessary work for yourself.
Sorry this post was so long! hope it helps