What's the best structure for an essay?

In A-level Psychology the strucure of the essay serves as a major component as to how many marks you will recieve. 

The key structure is as usual an introduction to give a brief background on the topic of interest and explain which key aspects will be discussed.

Each paragraph after that should follow the P.E.E format whereby you state the point, give an example and explain. Specificially in Psychology this involves stating a finding of research relevant to the question, giving a key study that backs up the finding using correct referencing, and then evaluating the study by giving the strengths and weaknesses using psychological terminology e.g. demand characterisitcs and whether it can be applied to the wider population or not. 

The conclusion wraps up the essay by leaving the reader with the key points to take away. Mention the strongest points briefly and link it to the original question. By following this simple strucutre, marks will be much easier to obtain.