Identify your ideas. Drawing a writing web or chart can help you get your ideas down on paper, and record exactly what you want to say in your essay. By knowing your topic, main ideas, and supporting details, you can start eliminating ideas that might be less important, keeping your writing focused and on-topic.
Organize your writing skeleton. A writing skeleton is simply the order of your paragraphs and ideas. Usually, a typical essay will have an introduction, three or four body paragraphs, and a conclusion. By knowing your form and the order you put your ideas in, you will know what order to write about them in your introduction paragraph.
Write the other parts of your essay. Sometimes writing the body of your essay, or even the conclusion, can help you write the introduction. By getting all of your points on paper, you can then pick and choose which aspects you'll address in your intro. It will also help you make the first paragraph, when you go back to write it, more inclusive and broader in scope.
Gather the topic sentences of your body paragraphs and conclusion. Now that you have written the rest of your essay, you can gather all of the main points from each paragraph to put into your intro. The introduction should include a wide overview of everything you will address in your paper, and for what purpose. Now that you know all of the things you have addressed, you will have a much easier time approaching the introduction.
Write your introduction. Don't copy your topic sentences verbatim, but try to summarize them in the order they appear in the body of your paper while writing your intro. You want to give the reader an idea of what is to come and why you are writing the paper. Ideally, your introduction should include the purpose of the paper, the topics of your body paragraphs, using language that interests the reader.