No one is asking you to memorize First Aid. First Aid is simply a resource that provides a concise list of things that are high yield for the boards, but you dont have to sit there and memorize it. I know that I cant. What I can do, is understand the conceptual reasons behind certain trends - for example, you dont have to memorize which class of drugs are effective against which bacteria, if you simply understand that some drugs have a mechanism of action or of entry that is blocked by a thick cell wall, you know that those are effective against gram negatives.
Only memorize the facts that you cant conceptualize for yourself. If you sit there and try to rote memorize 100% of the book you will do poorly, but instead if you are able to understand and reason out 50% of the book, you will know more of it in the future.
Also do UWorld questions, because the questions have answer explanations which can help with the understanding of first aid topics.
There are people who can memorize the entire book, but just because someone somewhere is able to do it, doesnt mean its right for you, you need to understand the kind of learning you excel at, and focus on applying those strategies to your studying ( I suck at memorizing, but concepts agree with me, so while I will memorize alot, I wont have to memorize everything because I will be able to understand and reason out significant amounts of everything).
Good luck