English GCSE Macbeth help PLEASE?

I have a controlled essay coming up and its a big one! Its to do with Macbeth , has anyone got any ideas on how to write it etc and what to include! I have treid reading the book but i cannot get my head round it! I have a target to get a C but i want to aim higher! I would be really pleased to get a B. But recently i haven't been doing to good with only achieving E's. I used to be really good but i've gone down so much now PLEASE HELP! THANKS!