How do I write a good introduction?

A good introduction should refer to the question, demonstrating to the examiner that you have understood what is asked of you. However, it is important that you don't just rewrite the question. You should use the key words in the question to establish where you stand in relation to it and then state the line of argument your essay will take. This may take a few sentences but can be kept brief, clear and concise, as you are not expected to relay every point you are going to make in your introduction. This will be done in the body of your essay and summarised finally in your conclusion.
Whilst you do not need to offer every idea you have in your introduction, you do need to convey your basic argument. In order to get the balance right it may be helpful to remember that by the end of your introduction the examiner should understand the direction your argument is going to take. Your introduction should 'signpost' the aim of your essay so you are able to refer back to it and expand on it in each paragraph, helping to keep your argument concise.