Pay special attention to your first sentence. Start off on the right foot with your readers by making sure that the first sentence actually says something useful and that it does so in an interesting and error-free way.
Be straightforward and confident.
Avoid statements like "In this paper, I will argue that Frederick Douglass valued education." While this sentence points toward your main argument, it isn't especially interesting. It might be more effective to say what you mean in a declarative sentence. It is much more convincing to tell us that "Frederick Douglass valued education" than to tell us that you are going to say that he did. Assert your main argument confidently. After all, you can't expect your reader to believe it if it doesn't sound like you believe it!
Sometimes, especially if the topic of your paper is somewhat dry or technical, opening with something catchy can help. Consider these options:
What Question(s) are You Trying to Answer?
Your entire essay will be a response to this question, and your introduction is the first step toward that end. Your direct answer to the assigned question will be your thesis, and your thesis will be included in your introduction, so it is a good idea to use the question as a jumping off point. Imagine that you are assigned the following question:
Education has long been considered a major force for American social change, righting the wrongs of our society. Drawing on the Narrative of the Life of Frederick Douglass, discuss the relationship between education and slavery in 19th-century America. Consider the following: How did white control of education reinforce slavery? How did Douglass and other enslaved African Americans view education while they endured slavery? And what role did education play in the acquisition of freedom? Most importantly, consider the degree to which education was or was not a major force for social change with regard to slavery.
You will probably refer back to your assignment extensively as you prepare your complete essay, and the prompt itself can also give you some clues about how to approach the introduction. Notice that it starts with a broad statement, that education has been considered a major force for social change, and then narrows to focus on specific questions from the book. One strategy might be to use a similar model in your own introduction —start off with a big picture sentence or two about the power of education as a force for change as a way of getting your reader interested and then focus in on the details of your argument about Douglass. Of course, a different approach could also be very successful, but looking at the way the professor set up the question can sometimes give you some ideas for how you might answer it.
You may think that you have to write your introduction first, but that isn't necessarily true, and it isn't always the most effective way to craft a good introduction.
You may find that you don't know what you are going to argue at the beginning of the writing process, and only through the experience of writing your paper do you discover your main argument. It is perfectly fine to start out thinking that you want to argue a particular point, but wind up arguing something slightly or even dramatically different by the time you've written most of the paper.
The writing process can be an important way to organize your ideas, think through complicated issues, refine your thoughts, and develop a sophisticated argument. However, an introduction written at the beginning of that discovery process will not necessarily reflect what you wind up with at the end. You will need to revise your paper to make sure that the introduction, all of the evidence, and the conclusion reflect the argument you intend. Sometimes it's easiest to just write up all of your evidence first and then write the introduction last—that way you can be sure that the introduction will match the body of the paper.
Don't be afraid to write a tentative introduction first and then change it later. Some people find that they need to write some kind of introduction in order to get the writing process started. That's fine, but if you are one of those people, be sure to return to your initial introduction later and rewrite if necessary.