(1) Research. It is the backbone of your major work. Select relevant sources that would be effective to include in your essay.
(2) Always make sure what you are discussing is about how the historians perceive your chosen event/personality.
(3) Be critical about the historians you have chosen. Why do they perceive your chosen event/personality in the way that they have?
(4) Footnotes are good for clarifying and are not involved in the word count. I would advise you use them as much as possible. Assume that the marker knows very little about your chosen event/personality.
(5) Quotes are useful if they help support your point. For example, you can use a quote that reflects your historian's bias.
(6) Ultimately draw to a confident conclusion. Sitting on the fence should be avoided unless it really is appropriate to the event/personality you have chosen.
(7) In drawing to a confident conclusion, make sure this conclusion actually answers the question you have created yourself. Do not derail. After all, you would have spent all those months trying to find an answer to such a question.