I felt the most difficult sections were FAR and REG since FAR and REG have the highest fail rates.
There is a lot of information to memorize, but more importantly for REG CPA USA is how to apply that information. REG exam focuses on federal taxation, business law, and business ethics. A major portion of REG deals with federal taxation.. I used Becker and passed REG CPA USA on first try. Becker has a very concise material- book and videos, in addition there are skills practice videos which focus on the key areas of the topic and plus many problems to go over. I went over materials may be 3 times and also kept solving MCQ's repeatedly.
You should be doing MCQs every day. This helps you understand the concepts more clearly and practice taking progress tests (a feature in the Becker Review) at the same time. One needs to have a brief idea of the authoritative literature for doing the research tasks in the task based simulations.
A week or two before your REG CPA USA exam date, do a final review to look at all the topics and focus on things you need to memorize or understand better. Doing this alone could raise your score. Once you are done with the final review take a mock which helps you assess your weak areas.
Best of Luck - Vinay