By the time a referee has finished the Introduction, they've probably made an initial decision about whether to accept or reject the paper -- they'll read the rest of the paper looking for evidence to support their decision.
A casual reader will continue on if the Introduction captivated them, and will set the paper aside otherwise. Here is the Stanford Info Lab's patented five-point structure for Introductions.
Whenever possible use a "top-down" description: readers should be able to see where the material is going, and they should be able to skip ahead and still get the idea.
In general a short summarizing paragraph will do, and under no circumstances should the paragraph simply repeat material from the Abstract or Introduction.
Thus, the notes include several exercises for the reader. The material in the abstract should not be repeated later word for word in the paper.
Titles can be long and descriptive: State the problem, your approach and solution, and the main contributions of the paper. (Exercise: Write an abstract for the multiway sort example.) The Introduction is crucially important.
Here are the notes from a presentation I gave at the Stanford Info Lab Friday lunch, 1/27/06, with a few (not many) revisions when I reprised the talk on 12/4/09, and no revisions for the 10/19/12 revival.
The presentation covered: As a running (fictitious!
Important components are: Running Example: When possible, use a running example throughout the paper.
It can be introduced either as a subsection at the end of the Introduction, or its own Section 2 or 3 (depending on Related Work).