The best way to study for the USMLE is to do practice test questions. There are a lot of USMLE-style question bank online, Kaplan, USMLERx, USMLExchange, USMLEWorld, to name a few. Doing practice test questions allows you to gauge your performance and helps you help familiar with the test format.
While studying your textbook and lecture notes (I assume you are in medical school) is also important, I find it more efficient to go through some practice test questions first when I start studying a certain organ system / discipline (again, I assume you learnt the materials at least once from lectures), then focus on specifics that I am troubles with. Most online question banks allow you to customize test sessions based on organ systems / disciplines. I also find that I learn a lot just by doing the practice test questions and reading the explanations.
One of the particularly good question bank is USMLExchange (http://www.USMLExchange.com). I like it because it does not require a subscription, that means you can use it for as long as you want. It is also very inexpensive and the test questions/explanations are excellent. You also get all the other performance tracking features, FRED-style interface, etc. Of course, if you can afford to buy a 6-month Kaplan Qbank subscription, that would be even better (Kaplan Qbank is sort of the gold standard).
The bottom line is, do practice test questions, find out what you need to work on, then work on it, and finally do several full-length tests before the exam.
Personal Experience. I am a medical student.