You can improve clarity by creating a pointed thesis that links directly to the question, carrying it through the entire essay and ensuring that the structure of your response is logical and cohesive. For instance, in one body paragraph, you should be able to make a point, provide evidence, elaborate on the evidence and then move on seamlessly to your next piece of evidence. Do not go on tangents. Try to explain concepts in a way that you will understand them and your marker will understand them. Whilst having a sophisticated vocabulary allows you to gain access to higher marks, ensure you fully understand the sophisticated words you want to use before writing because this in itself will improve the clarity of your response. If you have to, get to the bare bones of your argument without fluffing it up too much so that your point stands out.