A very important note for writing the introduction of a journal article, and I think it is useful for any article for that matter. Essentially four or five points:

• Start with a compelling question, story, data, quote
• Layout the map of the rest of the paper right there in the introduction leading to the next section
• Spell out the main argument in the introduction section, this helps to lay out the rest of the map of the paper together
• Use simple language.
• Use one of the two approaches or horses for courses - either write a rough sketch in the beginning and then rewrite, or write the perfect story right from the beginning. I like the former approach.