First - and this sounds really obvious but you'd be surprised how many people forget - read the question carefully. Does it look like a simple 'yes' or 'no' question (at A-Level, this is rarely the case)? Is it a question asking you to weigh up evidence (such as a 'how far', 'to what extent', or 'do you agree with the statement X'?). Let's take a random example: if we were answering the question 'Was the Protestant Reformation in England and Wales a genuinely popular phenomenon?', it is best to analyse the language in the question. We have key words: Reformation, England and Wales, genuinely popular. So your introduction would need to set out and define these terms. What was the Reformation, what was its impact in England and Wales, and what are you going to define as popularity (hint: popularity suggests that regular, ordinary people accepted the Reformation in their daily lives). You should then decide what you argument is and write it clearly at the top of your plan/page to keep referring back to while you're planning. It is always a good idea to split your argument into two or three main points, depending on the length of your essay. While it's tempting to present a two-sided argument - on one hand, it was successful and on the other, it wasn't - you'll gain access to higher marks by deciding on one line of argument and using points to back it up throughout the essay. So, for example, you could decide that the Reformation was not genuinely popular and have two points to support that, with corresponding evidence from what you have learned on your History course so far. This way of writing essays will stand you in good stead for when you write essays at university!