The previous posts are very sound. I would echo the idea of making sure that you know your topic. Preparation in a given area is critical and being able to convince the reader that you are competent in the field is important. In writing, I would suggest that answering the question in its entirety is going to be defining for success. Making sure that you sketch out an answer prior to composing it is important. When you create this outline in writing, make sure all pats of the question is answered before you actually compose the essay.
After having evaluated exams for 40 years, I can tell you what I'd like to see happen. First, make sure you take the time to understand the question. You'd be surprise how many students answer they question they hoped their instructor would ask rather than the one that was asked. Make sure you know what you're being asked to do: eg. provide 2 examples, compare 3 characters, etc. As soon as you understand the question, jot down the information that you know that will help you draft an answer. Make sure that information is relevant and that it answers the question. Then, and perhaps most importantly, just answer the question. Don't pad your answer with lots of interesting if irrelevant facts. You've been asked a question to see if you know some specific thing your instructor thinks is important; show the instructor that you do and move on.
Posts # 2 and three provide some very good advice on scoring good marks in exams. But most of this advice is limited to actions you can take during the process of writing your exams. However there is a lot you can do much before the exams start.
First thing is that you should know your subject well. This of course is greatly helped by regular and sincere studies through the term rather than just before exams.
Knowing is not enough. To score good marks, you should be able to put down in writing what you know. And this needs to be done in the time available during the exams. This ability differs greatly from person to person. If you are having difficulty during the exams in expressing yourself in well and in time, your preparation for exams should also include practice in answering questions in writing. Since time limit is important in exams, it is a good practice to mark the time you take in answering questions, and in case you are slow, practice more ti improve your speed.
Scoring good marks in the examination is not always simply directly proportional to your accumulated knowledge/information. Your preparation should be sound & thorough, but even then you must be right up to the occasion on the day of your examination. Don't worry & don't allow any nervous tension to get the better of yourself. From my long experience as a teacher and university examiner, I can offer you the following tips for your benefit:
a) Take some time to read & understand the questions so that you can choose the more suitable options to answer.
b) Try to be precise and organized so that you can answer appropriately & adequately, without any verbiage or roundaboutness.
c) Always substantiate your answer with examples from the primary text and some relevant critical references.
d) The first question you answer should be your best prepared answer. It produces good impression in the mind of the examiner.
e) If time permits, you can jot down your thoughts to make a rough draft of your answer.
f) Take good care of your spellings & sentence-construction. Revise all your answers before submission of script.
g) Time-management is very crucial in the examination. See that you have enough time to answer all your questions. Even one very good answer shall not compensate if you just leave out 1 or more for lack of time.
h) JUST KEEP YOUR COOL & BE CONFIDENT.