The best thing that you can do at this point is thoroughly learn your medical school coursework. You "review" for Step I but "learn" your coursework. You really can't do much of a review of what you haven't learned in the first place.
Thoroughly master your courses and then your review for Step I will be more efficient and useful. Depending on how your coursework is organized, classical curriculum, system-based curriculum or integrated curriculum; will determine how much useful information you have at this point.
Under a classical curriculum: Pathology, Pharm and Physio are the best represented subjects with Biochemistry, Behavioral Science/Biostats, Neuro(lots of this in Pharm) and Micro/Viro (lots of this in Path anyway) being the next most represented and Gross Anatomy being the least.
Under systems-based, you can review the systems that you have already mastered if you are totally bored so that you head into next semester with a solid background. Under the integrated curriculum, the same applies but you don't have to go system by system.
Any review done outside of prior mastery is not very useful and likely a waste of time. In short, review what you have mastered but not much more than that.