I'm also sitting this exam and hoping to get a high B/low A. I find revising from the CGP revision guide is really helpful. I literally didn't understand 50% of what I got taught in class (courtesy of a rubbish teacher) but this revision guide has really helped me.
Get a revision guide, READ READ READ, make notes.. DO PAST PAPERS!!!!
I've literally read through the whole guide like 4 times so far, and I don't plan on stopping!