If you've got notes that you wrote in class, they're good to study from too.

My strategy worked like this:

1. Re-read your notes.

2. Highlight the important parts - the lines, sentences, formulae that matter the most.

3. Re-read the highlighted parts of your notes.

For further help, write new notes: take the most important parts of your highlighted notes, and add any essential information from the textbook. Then, use these new notes and begin the process again. Eventually, you'll have notes that are condensed and refined, allowing you to revise a whole year's worth of material in an hour or so