Start now and begin by reading, JUST READING, the past exam questions and answers from either the ACCA website (preferable) or the questions / answers included in a reputable revision kit.
When you have read them all, read them again.
And again, and again, and ag….
You will find that there is a substantial degree of repetition in the questions and there’s no reason to believe that that repetition will not continue into the future.
In fairness to the examiner, this IS a law exam for accountants and the level / depth of law that you expected to know is quite superficial. With that in mind, the examiner’s hands are pretty much tied with reference to the breadth of the potential syllabus that he can ask