Here is an example of a 4 week study schedule for USMLE Step 1. This is the study schedule I used to review for Step 1 and ended up doing very well. This study schedule uses First Aid and UWorld Step 1 Qbank. I recommend these review books to supplement your First Aid reading.
Notice that the primary focus in this example is doing practice questions, as they are the most effective study tool. The reading material is less important and you will be moving very quickly through First Aid.
This is assuming that all the First Aid content is a review for you as you should have already learned it in medical school. If you did not do well in your first two years of medical school, especially in pathology and physiology, you may need to spend some extra time in First Aid and the review books.
If you feel that 4 weeks is not enough time to prepare, anywhere from 4-6 weeks may be better for you. Simply adjust the number of questions and reading accordingly, but keep this basic schedule, doing at least 3-4 full practice tests using UWorld questions prior to your exam.