Select an interesting, startling or unusual fact about the topic and include that fact in the first sentence or two. This will effectively grab the reader's attention by pointing out something he did not know. Alternatively, write a brief summary of the topic in the first sentences. Not every topic will have something startling to give it a boost, but a brief summary to lead up to the thesis is appropriate as well.
Write one or two transitional sentences. For example, if the original sentence or two gives a fact, the next sentences should transition from the fact to the point of the essay and the thesis statement. If the original sentence was a brief summary, it can continue into the next sentences, because the summary will require more than one sentence in most paragraphs.
Put the thesis at the end of the introduction. The thesis is the statement of the point of the written work. A thesis gives all the main points of the paper in a brief statement. For example, in an essay on Shakespeare's "Romeo and Juliet," a thesis might state, "Romeo was originally a fickle young man, but his love for Juliet changed his wavering nature." This sets up the essay to discuss why he was fickle and how falling in love with Juliet changed him.