Use rhetorical questions. If your essay is about childhood obesity, ask a question such as, "Why don't children in low-income families have equal access to places where they can get more healthful foods?" This gets the reader thinking about possible answers to the question and builds anticipation during the essay.
Include some of the results of your research in the introduction. This lets you start the essay with credible information as the basis of your thesis statement.
Stick to the subject at hand. Don't cram in too many ideas unrelated to the thesis statement, which would confuse readers and throw you off the track while you're writing. This is why during the research process you should narrow your topic.
A clear thesis will set the foundation for the rest of the essay. If you're arguing against the implementation of standardized tests as a high school graduation requirement, your thesis statement could be that standardized tests do not accurately measure whether students acquired the necessary academic skills for college and the work force.