What do I need to include in an essay?

You need to remember: context, analysis, writer's method/technique and spelling/grammar (watch out for common errors such as confusing: their, they're, and there, and also focus on your punctuation to let you be to the point and clear). You could make an acronym such as: CAWG (context, analysis, writer method and grammar), and write this on the side of your essay/exam response to serve as a physical reminder to keep doing these things and checking them. The other thing needed is a clear structure to your paragraphs which is largely achieved through avoiding over-complicated points - simply state your argument, give a bit of evidence, explain the relevance of this evidence and then link back to the question you have been asked. Keep asking yourself: "why is this relevant?" as this will let you maintain focus on the question at hand to tailor your response accordingly.