An anecdote -- a short, perhaps amusing account of an incident -- is effective at drawing the reader into your paper. An anecdote can entertain or make a point. The narrative nature of an anecdote appeals to the reader's emotions while introducing the topic. It's best to use an anecdote when you have an interesting story to tell. Keep the story brief and use vivid descriptive language.
An analogy works well for complex or unfamiliar subjects. Compare the topic with something more familiar to the reader, emphasizing the like features of the two subjects. Not only does this help the reader understand an abstract idea, it sets the tone for the rest of the paper, making it clear and easy to follow.
Irony is a discrepancy between what is expected and what actually is. A paradox is a statement that seems contrary to common sense, but may be true. Using these elements will stimulate the reader's interest. They set a philosophical tone for the paper.
Use of a thought-provoking quotation, a challenging question or a little-known fact about the topic can draw your reader's attention. These elements work well to engage your reader and draw her in emotionally. Verify that the information you use is true and use it illustrate the point of your essay. Don't summarize the entire paper in the introductory paragraph, just introduce the topic.