How should I structure the introduction to my exam essay?

Your introduction should clearly outline the points you will go on to make in the main body of the essay - the idea is to give the marker a good sense of the structure and purpose of your essay. Start with the main argument that you've chosen to make - "this essay argues that Peter the Great's administrative changes were the most important factor in his victory over Sweden", for instance - before then outlining each individual point you're going to use in it's defence. A good way to think of it is to have one sentence in the introduction for each paragraph of the essay itself. Efficiency is key - don't waste time with broad waffle. If the question is 'What was the most important factor in Peter the Great's victory over Sweden?', you don't need to repeat the question or summarise what Peter the Great's victory over Sweden involved, like 'Peter's victory over Sweden is considered by many to be a landmark moment in Russia's rise to military dominance.' This kind of sentence gets used a lot, but it doesn't actually help you answer the question, and so you shouldn't waste your limited time on it. The overall structure should therefore look like: 'argument: reason a, reason b, reason c.' Once that's done, you should launch straight into a paragraph elaborating on reason a.