this is probably the most horribly designed exam you will take your whole life, so the formula for most seems to be:
1. YOUR BIBLE: FIRST AID FOR THE USMLE--know everything in it and you'll be pretty damn good
2. UNDERGROUND VIGNETTES: you gotta know how to apply all the info in the above book to "clinical" situations
3. whichever review course you take--if you take one--use whatever they give you
4. LOADS of PRACTICE QUESTIONS--by now there are plenty of COMLEX practice questions floating around..i recommend the NMS USMLE practice book..erie, but what i scored on all those practice exams was damn close to my COMLEX score and the USMLE questions were a lot more detailed.