An essay puts forth a viewpoint, so think of it as structuring an argument.
1. Begin by writing an introduction that is general and introduces the topic. In your introduction, include a thesis statement that makes your position clear.
2. Write as many paragraphs as you need to make all the points of your argument. Begin each paragraph with a topic sentence that does two things: supports your thesis and controls the content of the paragraph it heads.
3. Be sure to establish your credibility. This is called ethos. Make your audience aware of what qualifies you to speak on the subject.
4. Make sure your position is reasonable, logical, and supported by factual information. This is called logos.
5. Engage your audience by appealing to the appropriate emotions for your subject. This is called pathos. The words you choose (diction) create your tone, and it, too, should be appropriate to your subject.
6. In your concluding paragraph, don't simply restate your main points. This is a bit insulting to your reader. A more effective way to end is to once again turn to more general terms, but rephrase your thesis. Rephrase, but don't repeat, to cement your argument.
7. Be sure your grammar, usage and mechanics are clean. Proofread carefully and seek an edit from someone you know to be a good writer. Be open to their edits and willing to revise.