Write the introductory paragraph. This should provide the background of the topic you are writing about, such as historical context, basic description, and why it is important. If you are constructing an argument, it's important to include a strong thesis statement. This statement communicates your opinion and introduces the evidence you will use to support it.
Write the body of the paper in your second paragraph. Use this paragraph to elaborate on the topic and examine it in greater detail and depth. If you are writing a thesis paper, this is where you present and analyze your evidence, which can take the form of facts, examples and arguments.
Write your concluding paragraph. It should offer a summation of the topic, and/or reframe the argument you made in your introduction. In a thesis paper, the conclusion should highlight how each piece of evidence presented in the body of the paper supports and validates your thesis statement. Make the last sentence as persuasive as possible.