Restatement of Thesis
The conclusion paragraph should restate the thesis. To be most effective it is recommended that the writer use language that "echoes" but does not duplicate language used throughout the paper.
Summary and Synthesis
The conclusion paragraph should also include a brief summary of the main points of the arguments made throughout the paper. This should not just be a regurgitation of information the reader has already encountered. Rather, this part of the conclusion should demonstrate how those main arguments fit together.
Things to Avoid
The thesis should not appear for the first time in your conclusion. This paragraph is also not the time to introduce new arguments or topics. In general, try to make sure that the language and arguments in the conclusion are not opposed to those in the rest of the writing.
An effective concluding paragraph should leave the reader with a clear sense of finality. Called a "call to action" in persuasive essays, this final thought should be as attention grabbing as the introductory sentence at the beginning of the writing.