just do a lot of exercises..

It depends on the class. Some classes give you study guides.
I wouldn't read the text book. I'd read and look over summaries, notes, and classwork/homework.
Later on, write the info you don't know onto flashcards and review it.

I always found it helpful to be able to draw charts of some sort, or diagrams. Then just redrawing the diagram or filling in charts.

I use the website Quizlet, it's really good!

For me it depends on the subject. For example math I redo previous problems. Literature classes I review summaries of longer texts and reread short ones. For foreign language classes, write out vocab and grammar over and over again.