I was recently forwarded (what I think) is a guide full of excellent advice, [*Writing Tips for Ph. D. Students* by John Cochrane](http://faculty.chicagobooth.edu/john.cochrane/research/papers/phd_paper_writing.pdf). In it, Cochrane has a brief section of advice on the introduction:

>The introduction should start with what you do in this paper, the major contribution. You must explain that contribution so that people can understand it. Don’t just state your
conclusion: “My results show that the pecking-order theory is rejected.” Give the fact behind that result. “In a regression of x on y, controlling for z, the coefficient is q.”
>
>The first sentence is the hardest. Do not start with philosophy, “Financial economists have long wondered if markets are efficient.” Do not start with “The finance literature has
long been interested in x.” Your paper must be interesting on its own, and not just because lots of other people wasted space on the subject. Do not start with a long motivation of
how important the issue is to public policy. All of this is known to writers as “clearing your throat.” It’s a waste of space. Start with your central contribution.
>
>Three pages is a good upper limit for the introduction.

This just reiterates the point both Oldboy and Suresh made that the introduction should clearly state what the paper is about, and also some more detailed advice about avoiding generic intro. statements. (Note the upper bound is good for social science articles that may be from 20~40 pages, it should be much lower for briefer articles in different fields or journals.)