Cross-post from an answer on quora.
Memorize all the amino acids. This one place of the few places where rote memorization is fruitful on the MCAT. Example of my notecard below.
Make, or buy, a map that interconnects all of the different metabolic pathways.
You should be able to work your way through this diagram knowing all the rate limiting enzymes and general features of the pathway
Read nutritional science primary literature, specifically about diabetes and insulin if you can find it. The MCAT tests applied biochemistry i.e nutritional science more so than foundational biochem.
Reference: I am an Altius MCAT tutor. check outfor data on what Altius students and tutors score.