See and for model introductions.

Action Introduction: An Action Introduction takes the reader into the middle of an action sequence. By not building up to the story, it forces the reader to read on to find out not only the significance of this moment in time, but what led up to and followed it. It is perfect for short essays where space must be conserved or for narrative essays that begin with a story.

Strong introductions tell the reader how the upcoming  will be organised.

In the introduction above, the opening line does not serve to grab the reader’s attention. Instead, it is a statement of an obvious and mundane fact. The second sentence is also not very specific. A more effective attention grabber may point out a specific, and perhaps surprising, instance when adults use math in their daily lives, in order to show the reader why this is such as important topic to consider.

The introduction to an essay should:

This essay in addressing the advantages and disadvantages of, … will focus upon, …

This can be as easy as outlining the major points that your essay will make on the way to the conclusion. You don't need to go into much detail in the introduction: just signal the major ‘landmarks.’

How to Write an Essay Introduction in 3 Easy Steps - Kibin

Most papers have outright thesis statements or objectives. Normally you will not devote a separate section of the paper to this; in fact, often the thesis or objective is conveniently located either right at the beginning or right at the end of the Introduction. A good thesis statement fits only the paper in which it appears. Thesis statements usually forecast the paper’s content, present the paper’s fundamental hypothesis, or even suggest that the paper is an argument for a particular way of thinking about a topic. Avoid the purely mechanical act of writing statements like "The first topic covered in this paper is x. The second topic covered is y. The third topic is . . ." Instead, concretely announce the most important elements of your topic and suggest your fundamental approach—even point us toward the paper’s conclusion if you can.

Here are two carefully focused and thoughtfully worded thesis statements, both of which appeared at the ends of introductory paragraphs:

How to Write an Introduction for an Essay | Pen and The Pad

As examples of how creative an introduction can be, here are the opening lines from a geography paper and a paper on optics, both of which use narrative technique to arouse our interest. Note how the first excerpt uses an "I" narrator comfortably while the second excerpt does not use "I" even though the writer is clearly reflective about the subject matter. The first excerpt is from a paper on the generic nature of America’s highway exit ramp services; the second is from a paper on shape constancy.

How To Write an Introduction: Structure, Tips | EssayPro

In brief, a paper’s introduction should define and limit the paper’s scope and purpose, indicate some sense of organization, and, whenever possible, suggest an overall argument. Another important principle in technical writing is that the introduction should be problem-focused, giving the reader enough background so that the paper’s importance and relationship to key ideas are clear. A rule of thumb about the introduction’s length: about 5-10% of the entire paper.