Only memorize what you absolutely have to.Most of the time you aren't expected to memorize an entire textbook word for word or every single part of the human body. If you're not sure what facts, figures, names, and dates need to be memorized by rote, ask the teacher.
Compare what you are trying to remember to something else.Ask yourself what this new fact or word or date reminds you of. Maybe to you, the American Civil War seems like football, which happens to be your favorite sport. When you think of it that way and imagine the generals as being team members for the Union and the Confederacy, you have an easier time remembering their names.
Organize the material you are learning by finding patterns in it.For instance, if you are working on memorizing the bones in the human body, your job will be easier if you group the information together, studying all the hand bones together, then all of the foot bones, and so on.
Rehearse what you have learned.Practice makes perfect. One way to rehearse is to have someone quiz you about what you read or were supposed to memorize. On your own, you might want to practice writing the information, whether it be dates, names of the parts of speech, or your spelling words. Rehersal works best if you make it a part of your studying. Ask yourself questions and practice recall after learning small pieces of information.