History GCSE is mainly about demonstrating a depth and breadth of knowledge of the relevant factors relating to the question. To move up to A Level standard work you should aim to show how these factors - for example foreign policy and religion - relate to each other and judge which ones are most important. Many A Level mark schemes also stress change versus continuity over time, so assessing how historical considerations, e.g the power of the monarch, change or don't change over your course is a good way to hit top marks. Keep the basic structure of GCSE essays though, retaining a strong sense of argument and counter-argument, and if you combine this with more A Level-style analysis your essay will be very strong.