A well-rehearsed production
Don't think of a paper as something that tests your ability to 'think on your feet' or that requires you to think up great new arguments on the spot. Think of it instead as a stage upon which you will display some of the arguments you have generated over the last year.
Show that you know the material by using it as a tool for your own arguments.
In addition to the content of the lectures, past papers are a pretty reliable guide to future papers, scepticism about the induction not withstanding. Notice that the questions tend to be the 'big' ones making it relatively easy to prepare in advance. However, past papers should be used with caution, and in consultation with your supervisor.
Make your own moves
History and Philosophy are not regurgitation, not even clear and elegant regurgitation. You should have something of your own to say on all the questions you prepare. Some students suppress their own arguments when answering paper questions, feeling that it is safer to stick to the reading and the lectures. Nothing could be further from the truth: it is far better to attempt your own argument, even if it is flawed, than only to give the arguments of others. Show that you know the material by using it as a tool for your own arguments.
Don't write for the lecturer
Even when you are reporting the views of others, use your own words. Show the examiner that you have made the problems your own.
Answer the question
Give the question some thought before you begin to write. Does it carry any presuppositions you do not accept? If so, pointing this out will impress. Don't include material that does not help your answer just because it is in the same general area and you happen to have written an essay on it. For example, if the question asks for the best solution to the problem of induction, you should not discuss all the worst ones. If the question asks for your view, don't just give someone else's. For example, if the question is whether there is such a thing as necessary connection, don't just explain why Hume thought not.
Avoid breathless lists
Your answer should be clear, coherent and progressive. Don't simply list all the vaguely relevant points you can think of. You are out to make a case, to convince a judge. Better to make fewer points in a tight, persuasive way, than to throw up too much too quickly and in no particular order.
Make an outline before you start to write, so you have a sense of structure and of how much you want to cover. Keep an eye on the clock, since it is rarely a good idea to spend much more time on one question than another and your class will suffer if you fail to answer a question or only give an outline.