You can write your introduction last. At that point, you will know the central purpose of your paper and the fully developed direction or claims you have created. Now you can write an introduction that will set the context for the thesis your wrote and the arguments to come.
If your paper is short (for example, five pages) do not use an extended introduction. You may want to use only a paragraph to set the context for your thesis. (Remember: do not set off the thesis in a paragraph of its own.) Your introductory paragraph is the first impression your reader has of your message; take time to make a clear, direct, complete, and understandable communication. The thesis should be an integral part of the introduction. In fact, the purpose of your introduction is to move your reader to the starting point that is your thesis. Avoid wasting words saying, "I decided to write about . . ." or "I agree with the statement that . . ."
If you are writing a longer paper (for example, twenty pages), you may want to write two or three paragraphs of introduction. Assess the length of the introduction by the kind of topic you will be addressing. For a more controversial, more complex, or more obscure topic, you may want to write an extended introduction to be sure you orient your reader sufficiently.
In the opening of any paper, avoid separating the reader from the content with sentences such as, "I am going to write about Number 13." Instead, directly address the content of the essay, such as "Toulmin's model of argument fails to include nonverbal elements of argument; the model focuses only on claims, data, and warrants as they occur linguistically." Although you want to address the content directly, you may want to embed this thesis in a paragraph of introductory remarks that help the reader understand the context in which it resides.
Avoid clauses and phrases that make broad generalizations or sweeping observations. Instead, construct sentences that specifically introduce the particular topic you have selected. Toward that end, avoid statements like, "Effective communication is important for each person's life" or "Rhetoric touches everything in our world." Instead, start the essay or paper at a point closer to the topic you want to address.
Ultimately, your goal in the introduction is to establish your thesis with both a specific topic and a well-defined direction or claim. You should be able to point to a single sentence in your essay which, when read alone, would concisely capture the topic and the direction or claim of your paper. The first line of your paper needs to be in direct line with that goal. The introductory paragraph(s) needs to be cohesive, moving the reader steadily toward the idea in your thesis. You do not need to be glib; you need to be clear and directed. The introduction should prepare the reader to arrive at your thesis.