My test is on June 4th, but I started studying back when we started having final exams a month ago. I studied for our final exams in those subject areas (path, pharm, micro, behavioral) and after finals I've gone back over first year subjects and miscellaneous stuff like genetics, embryo, and biostats. As of today I've been over everything by subject area once, and I'm going to do one more quick pass in the next week and a half over those materials again. This way when I start my last two and a half weeks of prep by organ system, I'll have seen everything twice and I can better put things together in a "big picture" way. Also during the first run through (which has taken much longer, being the first time through) I did questions based on subject areas and have recently started doing blocks of random questions now that I've gotten through everything once.
I think it helps to have seen everything at least once (that is twice, with once being when you actually learn it the first two years) before studying by organ system (at least in my head anyway) so that, as MrBeauregard said, you can better incorporate information into topics that encompass more than one discipline. Regardless, I think it helps to study it both ways at some point during step prep to make you think about things in multiple ways.