How to write an introduction?

Whatever you are writing—an essay, a report, an article, a thesis, a journal, a literature review, or any other piece of academic writing—the introduction will be the first thing the reader sees. If an introduction is poorly written or constructed, if it is boring, if it does not tell readers what they need to know, if it does not help readers to orient themselves to your paper—then you have lost your readers' goodwill right from the beginning, and can be sure of losing marks, no matter how well the rest of the assignment is constructed.
It’s essential, then, that you get the introduction right. This means that you must know what the introduction is supposed to do, what sorts of things must go into the introduction, how to write and structure the introduction properly, and how to interest your reader from the start.
An introduction should do the following:

• alert a reader’s interest
• indicate the scope and direction of the paper, and act as a navigation guide to its reading.
• show the reader how you are interpreting and approaching the question
• provide a context for the main issue
• indicate the focus of the paper
• indicate your conclusion and point of view

Further reading http://www.canberra.edu.au/studyskills/writing/introductions