Compartmentalize your plan of attack on the subject matter. Do not simply dive in and hope for the best. Break the body down into systems such as the nervous system, endocrine system, renal system. Then study those systems independently. It is easier to understand the body as a whole if you understand the basic functions of each cell, tissue and organ.
Quiz yourself after each topic to ensure you have not only reviewed but retained the information. The vastness of the human body coupled with its intricate design makes it imperative that every topic be understood fully before moving on to the next. Missing one concept can keep you from understanding other processes later in your studies.
Take breaks every hour or two, and spread your learning over the entire semester if in school. There is a reason schools work in four- to five-month semesters and not four week classes. Cramming for information is not only ineffective, but processing so much knowledge at once can lead to confusion and interfere with subjects previously learned. You simply can not retain the knowledge if it is reviewed too quickly. Human anatomy and physiology is especially difficult as many of the names and processes use Latin words that will further complicate knowledge retention over a short period of time.
Go back and review materials to reinforce the learning process. Just because you previously successfully reviewed a topic does not mean you're finished with it. Knowledge that is not used is lost, and this is especially true while studying. Even the most astute doctors and health professionals have copies of "The Physician's Desk Reference" and other publications right on their desk. Information must be reviewed periodically to keep it fresh and readily retrievable from your mind in the future.