Haven't taken it yet (Jan), but from friends who have they've said the OMM was very straightforward and it was pretty obvious when you were expected to use it, either from the cc or the patient prompting you.
Does your school do a review? If not I'd say just get with a friend and review the basics, structural exam, choose a tx like muscle energy and practice using that on different regions. I don't believe you can do HVLA so go over things like ME, FPR, inhibition, etc...