Introduction: In the introduction make sure you outline your arguement - it is important to have a strong arguement and to then outline the points you are going to discuss in the essay. Remember a history essay often asks you how far something was or to what extent - these type of questions want you to weigh up the question and give a balanced arguement.
The main body:
You should have about 3-4 paragraphs in which you adress 3-4 points. Make sure each paragraph begins with a clear line of arguement - you do not want to waffle - examiners hate this. Be direct with want you want to say. A good way to do this is by using PEEE - point, evidence, explination and evaluation.
First give your point - direct and concise.
Evidence - how can you support this? what happened in this time period etc
Explanation - explain how this links to the question and how it answers it the question.
Evaluation - give a mini conclusion - summarise your point.
Conclusion - Do not make this too long, a conclusion is not a repeat of what you have just said in your essay. The conclusion is important make sure that you have given your answer to the question - do not sit on the fence - give an answer that sumarises what you have been talking about throughout the essay but actually comes to some conclusion!