DNA-RL,
I'm a third year osteopathic student and I'll tell you what I did. I took both COMLEX and USMLE.
COMLEX
It almost is like a Step II exam in that they ask a lot of dx and tx questions. If you have a class right now that teaches Internal Medicine or principles of medicine, I suggest that you go to those classes and jot down some notes into whatever study guide you'll be using (FA, Step up, ect). I know some MSII's stop going to classes and concentrate on board studying, but osteopathic schools really gear their classes towards the COMLEX (at least my school did). The OMM part isn't very bad, just know sympathetic/parasympathetic levels and just learn about proper dx. Treatment will be REALLY straight forward. I spent a day reviewing OMM. Hardly any biochem, a lot of pharm and path.
USMLE
The biggest thing I'd say is SAMPLE QUESTIONS and QBANK. It's a better written exam and will really test your knowledge. But whatever knowledge you have for COMLEX will be suffice for USMLE. Just spend some extra time on biochem, molecular genetics, and pathology.
The best advice that I can give is, don't spread yourself too thin. Your fellow students will use a various study guides. Just stick with 1 or 2 and know them cold (I just memorized FA for both exams). The trick while studying is to really understand the mechanism of things, don't just memorize words.
Sadly, there is no secret...to do really well is to just buckle down and learn it the first time during the first 2 years of school and use the last couple weeks to REVIEW the material and memorize little tidbits.
I started reading FA about 3-4 wks before COMLEX, spent a day on OMM, and then took another 1 wk to brush up on biochem, molecular, and path for USMLE. If you get Qbank, get the USMLE one (even if you end up just taking COMLEX). And, order the practice COMLEX exam from NBOME.
Good luck with your studying!