I'm sure we've ALL been in this situation with test anxiety. Everyone has their own reactions and methods to what helps them deal with it. Some do better when they cram until 3 in the morning, others do well when they go to bed by 10. The best thing is to figure out what works for you. Don't risk it and cram- because sometimes you'll focus one that one little thing you think you forgot during the whole time of the exam. I don't know exactly what class you're talking about; but
if it's math/chem/phys: do a LOT of practice problems
if it's a science/psych/sociology-type of class: memorize those terms!
To help understand concepts better- you can try re-writing your notes or drawing pictures/graphs-
What helps me avoid extra test anxiety is to NOT cram last-minute information the hour before the exam. There's only so much you can do- the best thing is to allow your brain to just settle with the info it held onto.
Whatever works for you will be fine!
Good Luck!
Reshmi Basu