How do I write a good introduction?

1. Briefly: why the essay question is interesting and important, and/or acknowledge the key focus of the question. 

2. How you will structure your essay - the main point of each paragraph.('Firstly, I will discuss...secondly...thirdly...)

3. The conclusion you come to using these points. ('These three points will demonstrate that...')

NB. For point one, a quick mention of key arguments in historiography shows impressive knowledge of th subject matter.