I'm sure there are books out there about this, but I suppose my big piece of advice would be to do your best to keep up in each class. Do the reading before each session and if you have a class that gives you problem sets to do, but doesn't require you to turn them in, be sure to do them.

If you're assigned a paper to write, break it up into pieces and make each one a goal. I went to college with poor study habits and improved them mostly through the "pain of procrastination" and failing a few tests.

I always found it helpful to participate in informal study groups, too.

I hope you get some more extensive advice than this.