Hi there,
I would say that a really good way for you to structure your essay is to have a look at the marking scheme, as this will provide you with information regarding exactly what the examiner is looking for.
In psychology, examiners are interested in seeing that you have really good knowledge of theories and explanations. I would always begin an essay by outlining the main feature of the essay (such as, the cognitive explanation for Anorexia Nervosa)concisely. I would then follow with studies that support and disprove this. I would then follow with evaluation and other theoretical approaches, whilst linking back to the question to show relevance.
I hope this helps,
Nina