How can I make sure that my essay is relevant to the question?

First, you need to be sure of all of your learning objectives: this is what the examiner is going to be looking for, and if you tick all the boxes, then you're on the right track! Incorporate this into your revision- it won't take long, but will make all the difference. From there, you'll have to plan your essay. Look at each word of the question. Simplify it yourself. What is it specifically asking you to do? Once you are completely sure of what is being asked of you, it will make it much easier to know what you should be including in your essay.