That means you must be clear, forthright and logical. To wit, after reading the introduction, I tend to stop and ask myself where I think the rest of the paper is headed, what the individual paragraphs in its body will address and what the general nature of the conclusion will be.
If I'm right, it's because the introduction has laid out in clear and detailed fashion the theme and the general facts which the author will use to support it. The following is an introduction of what turned out to be a well-written paper, but the introduction was severely lacking: The role of women has changed over the centuries, and it has also differed from civilization to civilization.
Given that, I would rewrite the introduction this way: This paper will trace the development of women's rights and powers from ancient Egypt to late medieval France and explore their changing political, social and economic situation through time.
All the various means women have used to assert themselves show the different ways they have fought against repression and established themselves in authority.
Even more important, they make the argument readily accessible to readers and remind them of that purpose from start to end. As the writer of an essay, you're essentially a lawyer arguing in behalf of a client (your thesis) before a judge (the reader) who will decide the case (agree or disagree with you).
So, begin as a lawyer would, by laying out the facts to the judge in the way you think it will help your client best.
Like lawyers in court, you should make an "opening statement," in this case, an introduction.
Then review the facts of the case in detail just as lawyers question witnesses and submit evidence during a trial.
This process of presentation and cross-examination is equivalent to the "body" of your essay.
Finally, end with a "closing statement"—that is, the conclusion of your essay—arguing as strongly as possible in favor of your client's case, namely, your theme. It's not a murder mystery, for instance, full of surprising plot twists or unexpected revelations. Instead, lay everything out ahead of time so the reader can follow your argument easily.