I found that med chem wasn't too terrible. Organic chemistry was more difficult than med chem in terms of thought application. Med chem was mainly a pure memorization class at our school. Med chem involved more memorization and organic chemistry, to me, involved a lot more thought and application. Of course, when we had organic chemistry we had a standard textbook with tons of practice problems to work thought. We didn't have any practice problems to work through in med chem-- I'm pretty sure the old exams saved me.
Med. chem involved lots of structure activity relationship stuff. Always know the SAR stuff backwards and forwards. If you can circle the active part of each molecule then you should be able golden. I recall seeing a hell of a lot of tertiary and quarternary amines in med chem. Also, if they show any mechanism of activation or toxic metabolite pathways those are almost guaranteed to be on the test.
In terms of practical stuff to know, definitely spend times on learning the method of metabolism. Professors love to ask questions about what CYP pathway a drug is metabolized by, and potential drug interactions. If a drug is a pro-drug, then it is guaranteed to be on the test. The professors also love to ask questions about stereo-chemistry. So if the drug has multiple stereo-isomers (eg warfarin and albuterol) which one is more potent.
I found med chem to be a pretty fun class. It is definitely an overload of information, but if you have a good memory it shouldn't be too difficult. Unlike therapeutics, I found that med. chem was rather simple in terms of critical thinking.