Firstly, you must analyse what the question is asking. For example, the question may be to outline and evaluate genetic explanations of OCD. The question is asking you to outline and evaluate, and therefore the answer needs to be split into two parts. The first part of the question is asking to outline genetic explanations and is worth up to 6 marks, and therefore you should aim to write 6 to 7 sentences using your AO1 knowledge. It is essential to use key words effectively and technical terms where appropriate, and to make sure that the answer flows coherently. The second part of the question is to evaluate genetic explanations of OCD. The evaluation part of a 16 mark essay question is worth 10 marks, and so 3 to 4 paragraphs of AO3 evaluation should be sufficient. The best way to structure each paragraph of evaluation is to use the PEEL method. PEEL stands for point, evidence, explain and link. In addition, to get into the top marking band you could add contradicting points at the end of a few evaluation points to show the examiner that you are considering a range of different perspectives. Finally, read through your essay a few times over to make sure that you have answered the question and have considered different viewpoints.