To write a good introduction, first re-read the question and underline any key phrases - try to really understand what the question is asking.
In your introduction you need to outline what your argument will be. This argument should be maintained throughout the whole essay by using your main body paragaphs to give analysis and evidence to back it up.
For the first line you can use it to provide a context or background to your argument.
Then provide your main thesis, or argument. This shows how you are choosing to answer the question and what your argument is.
You should then set out what your essay will look like in order that the marker can have a clear view of what is to come. To do this give a mini introduction into each of your body paragraphs, they only need to be a sentance each.