Your conclusion should revisit your thesis and the ideas raised in your paper, but it needs to do more than simply summarize them. Use the points raised in the body of your essay to create a deeper and more insightful version of your thesis. If you're having trouble doing this, the Writing Center at the University of North Carolina at Chapel Hill suggests playing the "So what?" game. If you find yourself simply restating your thesis, ask yourself "So what?" or "Why should people care?" This can help you develop a more emphatic way to restate your argument.
Another way you can go beyond concluding with a simple summary is to propose a solution to the issue raised, suggest actions the reader can take or discuss the need for further research into the topic. Treating your examination of your subject as the final word is like creating a big stop sign at the end of your paper. Instead, you want your readers to keep thinking about the issue long after they've stopped reading.
A good conclusion goes beyond the assignment's instructions or the fulfillment of a writing prompt. This is the place for you to convince the reader that spending the time to read your paper was worthwhile. Discussing the significance of your argument within a broader context and making new connections with related issues can convince the reader that your ideas are useful outside the confines of a classroom.
Avoid using trite, hackneyed phrases such as "in conclusion" or "in summary" to begin your closing paragraph.
Avoid using overly-dramatic or sentimental language to drive your point home. Basing your closing arguments on the evidence laid out in your essay is much more effective than making sweeping generalizations. At the same time, it's also important to avoid language that minimizes or trivializes your argument or your authority as the writer.
The conclusion is never the place to introduce new evidence or an entirely new argument. If a point is important enough to be included, give it a place in the body of the essay.