How should one structure a typical A level essay exam answer?

The most importance driving factor in your answer should be your argument, At the beginning of the essay, make it clear to the marker exactly what you think about the issue in the question. For example, if the question were 'How united was the United States of America in 1801?', then at the top of your answer you should clearly state your judgement on the issue; your judgement must be balanced and rooted in facts. For example, 'this essay will argue that, while factionalism did exist, overall, the United States was more united than divided in 1801.' 

Following this initial statement of your argument, the main body of the essay will substantiate your argument using selected and specific knowledge. In dealing with the question of US national unity in 1801, you could point to factors that show that while disunity existed, unity prevailed in 1801. For example: disagreements between those who argued for a strong central government (Federalist Party) and those who opposed a large federal government (Democratic-Republican Party) led to divisions; but the memory of the American War of Independence, the presidency of George Washington, and the common belief in the power of democracy created a greater sense of unity than disunity. When discussing each of these factors, you must provide specific evidence (such as the different ideologies of the Federalist Party and the Democratic-Republican Party) and always relate the factor to your overall argument.