Include a transition at the beginning of the conclusion that indicates that the paper is wrapping up. Avoid clichés or tired phrasings such as "in conclusion" or "as you can see" if you can avoid it. Instead, sum up the existing information using different words. This often means repeating the thesis in a new way that reaffirms the point of your paper.
Stress your intentions to the reader. This means helping your readers to leave the essay feeling or thinking a certain way. With a persuasive essay, this will be a call to action to readers to confirm or change previously held opinions. With an expository essay, readers should be considering your thesis and assessing your supporting statements.
Sum up your major points in the essay without simply repeating them. Instead, discuss the points you made in a broader sense that strengthens your argument. For example, if your essay focused on the argument that pets should be adopted rather than bought and one of your points was the number of adoptable pets in shelters today, discuss how every pet adopted saves a pet's life instead of repeating the fact outright.
Avoid introducing new information in the conclusion. Your paper should hit on all your talking points in the main body. If you are still presenting new information in the closing of the essay, then it is likely not done and can be expanded further. Contrastingly, you may choose to leave out some information that detracts from the significance of your other talking points.
Leave the reader with a clear understanding of your thesis. The thesis statement should be clearly defined in the introduction and your arguments should be supported throughout. The conclusion is no place to be introducing the thesis statement of your paper; instead it should reaffirm what has already been made clear to the reader.