People disagree about how to start an essay (see Clarity of structure). I think there are two things an introductory section should do, in the following order:
- Give an overview of the topic and a flavour of why it is an interesting or controversial one; sketch the big picture. Indicate where the particular piece of terrain you cover in your essay is located in the wider area.
- Provide a map of your terrain. State what you are going to say in your essay. Specifically, state what form the essay will take – what your main points are and the order in which you are going to cover them – and also state briefly the conclusion you are working towards.
See below for a sample of what I consider to be a good introduction to an essay: