As the last thing your readers see, the conclusion is the last chance you have to drive your point home. The way you do this depends on the type of paper you're writing and what you want you readers to do after they've read what you've written.
Some questions to ask yourself:
What do you want your readers to do with this information? How does your work fit into the larger conversation you're contributing to? What question or problems has your work answered or solved for your readers? What is the new state of the conversation your thesis participates in, now that your work factors into that conversation?
Often, teachers will tell you to restate your thesis in your conclusion, but once you're comfortable with that, you might choose to add to it. A way to think about how to expand on your conclusion is to think of it like the end to a movies plot:
Mystery/Solution (Bourne Identity): Does your introduction pose a question? Do your body paragraphs answer parts of a larger question? Try using the conclusion as a place to tie together the answers from your body paragraphs, like clues to solving a mystery, into an answer to the question in your introduction. Keep in mind that this can take more than one sentence to answer. It's taken multiple paragraphs to build to this, so take the space you need to tie it all together! Remember to tell your reader about the significance of your answer and how it affects them.
Commentary/Call to Action (Wall-E): Does your introduction focus on a problem for a particular group, society, scholarly field, or text? Do your body paragraphs explore the parts of the problem, possible effects, or solutions for parts of the problem? Try using your conclusion to propose your solution or a call to action. What do you want your readers to do to address the problem?
Plot Twist/New Perspective (Sixth Sense): Does your introduction present a situation, story, conflict, or apparent paradox? Do your body paragraphs present context and additional details that change the way readers can perceive the situation, story, conflict, or paradox? Try using your conclusion to reframe the situation, story, conflic, or paradox through the new insight your analysis has revealed.
Multiple Threads/Common Weave (Crash): Does your introduction set up an analysis of specific topic(s) within a larger category? Do your body paragraphs develop specific details, explore the way your topic unfolds, and explain the message your topic has at a local level? Try using your conclusion to show how the specifics of your analysis are examples of a larger phenomenon and generalize the local messages as a bigger picture "moral of the story."
Exploration/Future Possibilities (The Matrix): Does your introduction set up a situation that your body paragraphs explore and define? Try using your conclusion to predict where the conversation will go next, what further research is needed, what problems your exploration has brought to light and how they might be addressed in the future.