Back when I was studying for my "A" levels, I find it useful to spot topics and questions. Take a look at the past years papers and then categorise each question under a certain topic. After that take a look at which topic had the most questions asked. My greatest success was in History. I was suppose to do 4 questions and out of the 10/12(?) choices available, I believe I spotted 8 of them. Note that this does not mean ignoring other topics. You should still be prepared to answer anything thrown at you.l Spotting of course is also useful in Univerisity to a certain extent. But for exams prior to univerisity it is the most useful since it is rather easiest to spot. However, university exams have a higher chance of it being open book, which makes preparing topics even more effective. So what type of exam is it, open or closed? Of course this is most useful for essay type exams. Do not prepare essays as a full but rather prepare the points needed for answering that particular type of question.
And second advice, if you still have time after preparing the topics, is to do a bit of research outside of the syllabus for the spotted topics. Examiners seem to get a thrill out of reading something fresh. They would think 'wow, this student is great, she not only understand what is needed but studied extra.' Or prepare a interesting argument/opinion based on the facts learnt. So that after presenting the different points taught to you, you can offer your own opinion and criticism about the situation. The examiners woulod then think 'oh my koala bear! This student could think of such a good argument in the midst of the stress of an exam. She must be brilliant. Only an "A" for her will do.'
Prepare some quotes by famous people in that particular field. I use to prepare a list of quotes and try to use at least 3 quotes per essay. Make sure they are relevant and not 'forced.'
Third advice, if possible, try to provide headlines. So if that part of the essay is talking about let us say the theory of enterprise, so you would have: Theory: Adam Smith's Invisible Hand. Underline it. It makes it easier for them to read and also it provides a guiding light throughout your essay for the examiners. Depending on how you work, just before your introduction you should have a list of things you want to talk about. It could simply be all those headlines placed together like:
It structure and format to your essay. But if you are the type that thinks on the spot and do not really write fast, this could be skipped. This brings me back to my point on preparing the topics. Once prepared, all you have to do is to list the topics you want to talk about, so it does not take any time and prevents you from forgeting to talk about a certain point. Remember this should not be too long. Just a brief outline of the essay. Another advantage of this, although this is dependent on examiners is that if you did not have time to complete your essay, at least the examiner would know that you know your syllabus and that only a lack of time prevented you from completing it. And furthermore, the point form pre intro sets up a positive state of mind of the examiner even before they go into the body of your paper. They might think 'hmm this person knows what she is talking about.' That may make them read your paper in a more positive light.
Good preparation for everything since the more you prepare the more luck will come to you.