How would I structure a 24 mark answer?

Well firstly, you would have to break down your answer content into two sections: A01 and A02/3.

A01:

A01 is the 'explain' part of the question and is worth 8 marks out of the possible 24. This should always be written first in an essay-paragraph format. This would usually consist of 4-5 paragraphs, with one point in each, so making 4-5 points altogether. 5 if your answer is less descriptive, 4 if your answer is more descriptive.

A02/3:

A02/3 marks are the evaluative components of the question. Here you will usually make 7-8 points. Students usually always make the mistake of mixing A01 and A02/3 content together, and although you will still be credited for your content, you may lose a couple of marks due to strucure. You should ALWAYS write out all your A01 points and then all of you A02 points afterwards. 

Your A02 points should include 6 strong points including IDA concepts: Issues, Debates and Approaches. E.g. The cognitive approach to explain sleep walking, animal research and the 3R's to justify animal testing in psychological research, and the Nature vs. Nurture debate to explain the relative contributions of genetics and the environment to a psychological disorder.