The introduction to any piece, be it writing or any other form of artistic outlet, has to have something about it that grabs hold of the audience and makes them want to go further with it. Writing must stimulate the reader within a few sentences, certainly a paragraph at the most, to hold onto it’s audience. Say something that is unexpected or even controversial to get them interested.
If one were to find a book, web-page, essay, read the first paragraph and be bored by it, the thing most people will do after this is put the book back on the shelf, click off the page or find another essay that is a little more interesting. One way to get someone interest and make them want to read on is to say something they don’t expect in your introduction.
Given an essay question, personal opinion should not hold much weight if any, one should really be trying to appear as an objective peer to all and any that read it. Yet, if in the introduction, you were to personally disagree with a statement made in the essay question, this can in fact grab the attention of the reader and make then wish to read more.
The more recent view I have now taken is, an introduction should be all these things and a summarised version of an essay plan, which in my case, is developing as the essay is written. There should also be a lead into the argument you are going to produce. It should give your readers a good idea of where you are going with the argument and how you are going to get there.
I am sure there is more to it that all the above. If anyone else has any ideas about other ways to "grab the attention of your audience" please do leave a comment I would be most interested to hear.