Unless you are already an expert on the topic, do some research in the area of diversity and see what sparks your interest. Once you have determined a specific area of diversity you wish to focus on, determine the purpose of your essay. Will your essay be informative or persuasive? An essay can also be written to entertain, but that would be an unlikely purpose for an essay on diversity.
Once you have determined your topic and purpose, consider your audience. Who will be the reader of this essay? This will help guide your tone and language choice.
The next step is to write your topic or thesis statement, and then use your topic statement to create an outline that emphasizes the key points you wish to discuss in your essay about diversity.
Using your outline, complete a rough draft, using credible sources as references. Review your essay for cohesiveness, organization, and word choice, as well as grammar/spelling/punctuation. You might wish to have a peer review your essay as well and provide feedback.
Lastly, complete your final draft.