Brainstorm ideas for the essay. Write the subject of the essay at the top of the paper, then start a list of ideas that will be touched on in the essay.
From each item on the list, write three specific details. These details will become the three body paragraphs of the essay. Take an item off the list that is the least-interesting or may be difficult too describe. Remove items from the list one by one until it is narrowed down to the most interesting or easiest to write about topic.
Write the introductory paragraph of the expressive essay. Open up the paragraph with an "I" statement ("I feel the most important thing to ever happen to me is..."). Lightly mention the three details that were written on the list, then close it with another definitive statement about the topic.
Take one of the details on the list and use it as the theme for the second paragraph. Add lots of personal description sentences, pick out specific details and expand. Describe sights, sounds and tastes. Try to avoid stringing together too many adjectives together in an attempt to cover lots of space. Generally, use no more than 3 adjectives.
Repeat Step 4 twice more for the other details. Close the essay with a paragraph that is a summation of the details and tie them together into the theme.