The trick to writing an successful essay in the exam in the planning. Those first 5 minutes should be spend taking deep breaths and reading the questions carefully. It is a common mistake to see a topic you have studied well in an exam question and start answering it right away before you fully comprehend what is asking. It will be good to underline any key words (not the whole question though). You need to look at:
a) how the question is framed: is it a 'Discuss...' question, a quote that you need to agree or disagree with;
b) the chronological boundaries;
While reading the question you should also keep in mind your own knowledge and understanding. This will help you realise whether or not you will be able to answert the question effectively. You should ask yourself:
a) do I know events or individuals that I can base my answer on;
b) do I understand the turning points or continuities concerned with this question and which examples to use;
c) do I know a sufficient amount of primary and secondary sources to support my argument?
After deciding on a question, the next step is a brief plan. There you will write the first things that come on your mind, which are also likely to be the most important. You can refer to your plan when you are stuck and this will also help you to write an informed introductory paragraph.
REMEMBER: Do not make it difficult for your examiner to find your arguement. State it in the introduction. For example: "In this essay, I will argue that ... was indeed a turning point for ... because...'. Also give a brief summary of all the main point you are going to make.
Your main body works as evidence of what you have stated in the introduction. Every topic sentence should refer back to the question and let the examiner know this paragraph is relevant to what you are answering. Make sure that you tackle different aspects of the question and answer all its components! In each paragraph, give different reasons why your argument is correct and try to defy the opposing point of view.
In the conclusion, do not try to insert new information, but simply bring home your most convincing statements and wrap things up.
This may seem as a lot to take in and it takes some practise to decide on a question and make a fast plan. Practise makes perfect so it is always a good idea to try to solve some past papers but - be warned - do not try to answer your exam question in the same way you did the past papers. Each question is framed differently and you should adapt your evidence to what is asked of you.
I truly hope this helps and best of luck with your exams!