Lots of luck, more interest in medicine than that crap we had to learn in undergrad, and the knowledge of one Dr. Ed Friedlander M.D. He told me to understand it don't memorize it. That made all the difference. I passed the Shelf exam at the end of my first year, scored an equivalent of 215 on the Kaplan evaluation exam, right before Thanksgiving, took Kaplan, and smoked the real deal.
My only advice is to do what works for you find your weakness and fix it. Take shelf exams if possible. If you need more structure in your life for studying, take Kaplan. If not, get a good review book. If you have test anxiety, take a bunch of tests on the computer. Medschool.com used to have a test, but my second year roomate (who also uses DO/MBA) says that is a no go.