What do I have to include on a Romeo and Juliet essay to get an A*?

Well first, have your essay detail the basic plot, characters, and historical setting of Romeo and Juliet. Then perhaps you could pad out the essay with the "true allegory" everything is about. Lord Capulet is representative of The House of York, and Montague is representative of the House of Lancaster. Juliet is England, who despite the War of the Roses (a contemporary conflict of Shakespeare between York and Tudor) or the "feud", loves Romeo who is Wales. Their love is a unification of Wales and England, and only after their deaths (i.e. after all of the blood spilled in the War of the Roses by the people from the respective countries) does the War of Roses gets resolved and Wales and England becomes united or the "feud between the families" is ended. Not only would this be putting allegory into the play, it adds social and historical context. You can come up with your own allegory if you want.