How can I reach top band marks in my essays?

What you're looking for is to be as analytic and succinct as possible. A lot of people struggle to not just describe events and tell a story. What's more important are your judgements and those of historians. You need to be extremely critical of every sentence you write before you write it. Ask yourself, what I'm I trying to prove here? and how is this sentence serving that greater purpose? Rather than just filling the page with the content you've memorised. To hit the very highest marks make sure to include the views of published historians and don't be afraid to critique them, this will show your confidence and expertise in the subject matter.