Although this guide is made for A2 students, maybe AS students can also benefit from it. There are short essay questions in the AS exams.
DO make a brief introduction (one short paragraph should do it) and a slightly longer conclusion. A good portion of your essay should be dedicated to the body.
DO use plenty of terminologies. Just stick them where you can fit them.
DO signpost in your introduction (e.g. "In this essay, I will be discussing/assessing...)
DO give a brief description of your topic in the introduction.
DO quote from books, but be sure to cite the author, the year, and the page.
DO give examples to strengthen each of the points you make. When giving examples from researches, give the name of the researcher (and the year, if you can).
DO give different perspectives if the question allows you to do so (different approaches to psychology, strengths and weaknesses, etc).
DO refer to your AS material. Show the examiners you remember what you have learned last year.
DO give a brief summary of the essay so far in the conclusion.
DO give your final answer/evaluation of the question.
DO clarify/reinforce your argument.
DON'T be too conversational. Remember, this is an academic writing. Be impassive!
DON'T ask rhetorical questions (e.g. "Can you imagine what we would do without computers?") Similarly, don't ask questions then answer them yourself.
DON'T use abbreviations without explaining them first. e.g. Write "supra-chiasmatic nucleus (SCN)" first, then you can write "SCN" for the rest of the essay.
DON'T assume the examiners always know what you're talking about. Make sure you explain everything clearly and guide them through each point you are making.
DON'T give personal opinions without sufficient evidence.
DON'T copy from books, other essays, and/or websites.
DON'T be too descriptive of the researches, unless the question requires you to do so. State what is relevant and be concise.
DON'T quote a whole passage. Put in key words/phrases.