Avoid rote memorization when studying. When you memorize bare facts without real comprehension, they're harder to remember. For example, if you're studying for a biology exam, don't just memorize your textbook's bullet points for the different stages of mitosis. Ask the teacher to explain to you exactly what happens until you can repeat the process in your own words. Check that you can answer questions related to the topic but not necessarily in the study guide. If you can speak and write clearly about the topic with no prompting, it indicates genuine understanding.
You can study for a dozen hours before the exam, but if it's noisy and your studying is interspersed with phone calls and chatting with friends, you're probably retaining very little. Study in a very quiet place without distractions so you can keep your mind on the material. Turn off your phone and the Internet unless you absolutely need it. If you're in a public place, put on your headphones and listen to instrumental music. Your recall will be much stronger when you're trying to reach information you absorbed in a focused environment.
Show yourself what you know at the end of every study session. Put away your notes and books and write about the material until you can't think of anything else to add. Don't just list facts; draw conclusions, form opinions and make connections. Ask a friend to listen while you speak about the material. Give her your book and have her ask questions. Get accustomed to speaking and writing without a prompt. When test day comes, you'll already be used to demonstrating your knowledge without a prompt.
Sitting at a desk for hours can dull your senses and decrease your concentration. Engage actively with the material and it will help you remember more during the exam. Make flashcards and go through them as you walk around the park. Put your study guide on the treadmill while you jog. Do yoga while you watch a slide show of art history images. Physical activity improves concentration and thus sharpens your ability to retain information.
When you have to remember a complicated process or set of characteristics in a certain order, a mnemonic device can help jog your memory on the exam. For example, if you need to remember the planets in order from the sun, memorize "My very educated mother just saw Uncle Ned's parrot." The first letter of each word stands for a planet. Write down your device on the test paper immediately.