step up is key, first aid is the baseline you must know, it covers the need to know facts, memorization facts that is. Step up is much the same, but it takes a somewhat more clinical approach that really helps with step 1 questions. I would also highly recommend high yield histology and molecular biology. I think people tended to shy away from these two, but they are the two books I think put me over the top into the 99th percentile.