Expository essays require that the the writer  give information, explain the topic or define something. To accomplish that,  they are best developed by the use of facts and statistical information, cause and effect relationships, or examples. Since they are factual, they are written without emotion and usually written in the third person. That means that the use of the pronoun "I" is not usually found within the essay.

     Expository essays also have a distinct format.

• The thesis statement must be defined and narrow enough to be supported within the essay.

• Each supporting paragraph must have a distinct controlling topic and all other sentences must factually relate directly to it. The transition words or phrases are important as they help the reader follow along and reinforce the logic.

• Finally, the conclusion paragraph should originally restate the thesis and the main supporting ideas. Finish with the a statement that reinforces your position in a meaningful and memorable way.

• Never introduce new material in the conclusion.

     Like all kinds of five paragraph essays, there is a specific format to be followed.

• The topic sentence cannot be a fact as facts cannot be debated. It should be a statement of position. That position must be clear and direct. This statement directs the readers to follow along with your logic towards the specific stated conclusion that you want them to support. Do not make it personal so do not use personal pronouns. Make it definitive. 

• Then, in the same introductory paragraph, state the three best reasons that you have to support your position as the remainder of the opening paragraph. These reasons become the topics of each of the three supporting paragraphs. Again, be sure they are able to be supported with additional separate facts. 

• In the body of the essay, the writer uses specific evidence, examples, and statistics and not broad generalizations or personal opinions to persuade the reader that the stated position is a valid one. Each topic sentence for the support paragraphs have been introduced in the beginning paragraph. Each additional sentence must closely relate to the topic and the sentence that came before it. This way, the logic of the argument is easy to follow.  
• Be sure to use adequate transitions between paragraphs as they make it easy for the reader to follow the logic of the presentation. 

• As one closes the essay, it is most important to to clearly redefine the topic and restate the most compelling evidence cited in original form. Remember, this is the last chance to remind the reader and convince him/her to accept the writer's position. 

• Do not introduce new material in the conclusion.