Give yourself a reasonable amount of time to memorize. Unless you have a photographic memory, cramming the day before is not going to be enough time to really get the information into your brain!
Break up the topic into subtopics. If you have to memorize psychology for example divide a list into famous psychologists, theories, basic definitions and so forth. This will help you to categorize everything you need to memorize and make it easier.
Use index cards. This was a lifesaver for me in college. I remember the time I had to memorize 100 paintings and the artists assigned to each. I also had to describe the painting and the symbolism etc. I thought, how on earth am I going to do this? So I wrote 100 index cards with a small symbol representing the painting, the artist and its relevance. For example, Van Gogh, Picture of a sunflower, and a description. These cards helped me ace that test as opposed to trying to memorize these paintings straight from a book!
Try memory tricks. As silly as it sounds making songs out of definitions and facts truly works. To this day I know what the definition of semi-permeable is because of a song my sister made up while she was studying science as a child!
Write, rewrite and write some more. My biology teacher wrote lengthy notes on the blackboard all of the time. I thought it was torture, but he used to say "If you write something down, you will learn it." He was right. So, try rewriting your notes as a means of studying and you will retain a lot of information.
In speech class, we learned another trick used by philosophers such as Plato. In ancient times, speeches were memorized by picturing a house. Certain areas of the house were assigned different passages. Then as the speech was recited, the orator literally walked through the house in his mind. For example, an introduction about War was placed at the front door. In his mind, the orator would picture the front door and remember all he memorized about War. The next chapter of the speech was about Armies, for example and that was assigned to the living room. And so on. By the time the orator finished his speech, he had mentally "walked" through the home. It sounds a little strange, but it works for speeches!
Once you think you've memorized everything, have someone quiz you. Hearing yourself say things aloud will definitely reinforce that you remembered everything and it helps you identify weak spots. I hope you remember these pointers, now go and ace that test!