You will need to proceed in stages. The first stage is the prewriting stage. Assuming that your essay is a description of your trip to the state fair, write down everything that you can remember about the fair. Ask yourself the following questions: What did I do? What did I see? Who was with me? After answering these questions, organize your trip chronologically. Write an outline.
Now that you have a rough outline, it's time to begin writing. One of the biggest challenges in a descriptive essay is taking your subjective experiences and making them objective. The phrase "It was so fun" says much more to you than it does to the reader. Explain why something was fun. Think of yourself as a reporter. You don't have to take yourself completely out of the descriptions, but you need to review whatever you're describing objectively so your reader can experience what you've experienced.
Go back through your essay and edit it for verbs and nouns. Do you use a state-of-being verb such as "to be" or "to have" when a more vibrant verb choice is available? Use meaningful and descriptive adjectives. We have five senses, and the more that you make use of them in your essay, the more the reader can relate to your experiences. Don't overwrite, however. Sometimes using a word like "said" is perfectly fine; don't feel that you must use a synonym, such as "declared" or "stated," for every instance. Adjectives can be overused as well. For example, it is a good idea to use colors to describe objects, but if you can, choose nouns that imply colors. Rather than writing about a light brown horse, you can note that the type of horse is a palomino, which is a light brown horse. Such a description allows you more flexibility and economy.
When you revise, pretend you do not know anything about what you describe. Read your essay aloud to yourself. Are some passages unclear? Have you added so many adjectives that you've lost the unique voice of the essay? Having others read it for you can be a great help.
Most essays you write in school will require you to include your thesis in your introductory paragraph. This method works well for argumentative essays, but not for descriptive essays. An alternative to the thesis in a descriptive essay is to add a interpretive conclusion. Write your essay according to the events of your outline. For your concluding paragraph, examine the entirety of your essay through the perspective of time and describe what you learned from the event, place or person. Even the simplest encounters in our lives can lend themselves to an insight. When you identify the insight, it creates a dominant impression on the reader, which, in the end, is what the reader will remember most about your essay. For example, in a descriptive essay about the fair, you may describe events of the day; then, in the conclusion, weigh that day against most other days. Is a trip to the fair just an escape from the drudgery of everyday life? Or did the trip make the fair seem comparable to daily life as an exciting carnival ride or a game of chance? Your conclusion will be important, so take care not be generic or cliched.