Hi Mary the Med Student- thank you for the advice!! Actually, I'm starting as a first year in August so I have a while. I just read this awesome book by Thornborough (how to be a successful medical student) and they suggest getting a USMLE book to study for tests....or at least get a glimpse of how one should be studying for exams.
I agree that you should study/read, basicly memorize every detail of First Aid. Almost every question I saw on the boards could be answered from that book. I would consider it the gold standard for Step 1. Some of my classmates also used Step Up and liked it. The charts in the back of Step Up were particularly helpful! Using a review book to study for tests is okay as a brief refresher the day before the exam, however it obviously would not provide enough detail to obtain a good grade. Best of luck!
If you're a first year student wanting to get ahead, I'd invest in some of the BRS (Board Review Series) review books--especially Chung's Gross Anatomy, Costanzo's Physiology (1st yr), and Schneider's Pathology (2nd yr). They are pretty in-depth reviews that are great for class test review, in addition to solidifying what's really important to know.
The benefit of this is that you'll already be very familiar with the books by the time to come to the boards, and your review will be more in depth than First Aid (First Aid is a great book, but I'd concur with other posters and say that it's not enough for a great score).
First Aid is no way good enough! My step had so much detail not on first aid... for example, I noticed lots of questions about specific proteins in viruses (eg: what protein does such and such virus use to uncoat itself... or something).
However, First Aid is a good starting point that you should supplement heavily. but honestly, I think the best way of studying is to study hard during basic sciences (unfortunately). There were several questions that I didn't remember from any review book, but I vaguely remembered reading about in a syllabus.