So do yourself a favor when you run into those horrible "weed out" classes and do the problems at the end of each chapter, or even go to the resource centers for your department to get hold of old quizzes or exams and use those about 60% (the other 40% being your own homework assignments and questions from the back of the book) in preparation for an exam.
Re-writing your notes is always a good idea too, but only if you can better absorb. Other methods that I employed included pretending to teach someone else the concept (lame, but it worked) and mnemonics devices.
Study groups aren't always great (e.g. my AP Chemistry group was mostly for Colts games and pizza), but if you can find people who want to work just as hard as you do (and with whom you can get along easily), go for it.
If you have any other suggestions, please comment! :)