Consider your audience. If you're writing for your own enjoyment, your audience consists of anyone who wants to read your work. Write the way you want. With a specific audience in mind -- such as a teacher, college admissions office or specific publication -- you can think more about what's appropriate and what might be well received. But it is more important to write the essay you want than the essay you think someone expects you to write.
Choose an overall topic. This is harder than it seems because you have your whole life to choose from. Stories you enjoy telling orally might be a good place to start, but a good personal essay requires more than a funny story. Readers are more demanding than listeners. Humor is good, but something else is also needed so that it appeals to a broader audience -- for example, emotional conflict or sociopolitical analysis. Think about what your story means to the reader. If someone who's never met you wouldn't be interested in your story, the topic is probably not a good one.
Outline. Decide where to start. Determine the topics you'll address and in what order. Starting from the beginning might be best, but starting at the end might be more interesting. Start with the part where you're stranded in the middle of the woods without any shoes, and explain later how your girlfriend drove off with the tent. Some writers prepare detailed outlines; some don't outline at all. Much of the writing process is a matter of personal preference.
Research your topic. Just because an essay is personal doesn't mean you know everything you need to know about it. Well-researched statistics, facts or historical anecdotes can improve the essay's quality.
Write your story. Don't stop to agonize over what you've written -- just keep moving. Cover the computer screen with a piece of paper and keep typing, or write on paper.
Include all the important elements of your story according to your outline, but don't be afraid to change the plan while you write. If it seems like something needs explaining before you move on to the next section, explain it. Your essay should flow. Each paragraph should contain a basic theme or idea and logically follow the paragraph before it. If you reach a point where you can't bridge the topical gap between what you've written and what you want to write next, that's OK. Keep going and worry about smooth transitions later.
Describe people, places and events in detail whenever possible. Unnecessary details can be taken out later. Show instead of tell. Don't say that a person was angry; say that his face turned red and he started shouting. Don't say that the house was ugly, describe why it was ugly.
Read over your story immediately after finishing it. Correct any grammar or spelling errors. If a sentence sounds weird, rewrite it or modify it until it sounds right.
Leave your essay alone for at least a day so that you have a fresh perspective when you revise later.
Reread your essay, preferably aloud. Reading aloud helps you notice when something sounds odd. Does everything make sense? Are there any unanswered questions or missing details? Does everything flow? One paragraph should transition to the next smoothly and logically.
Ask yourself what your essay is trying to say. Does it accomplish this goal? Does every paragraph work toward this end, or does it go off on unrelated tangents? Often, a writer doesn't know what he is really writing about until after the first draft. Don't be afraid to change things around as your essay takes shape. Poet Robert Frost said, "No surprise for the writer, no surprise for the reader."
Have friends or family read the essay. Ask them to look for grammar issues, but also ask them what they think the essay is really about. If their answer doesn't match your intentions, you might need to restructure. If they think the essay is about how it's important to be prepared for a camping trip and you want it to be about how extreme circumstances bring people together, maybe you need to write more about how you and your mother-in-law worked together to make a fire.
Focus on the paragraphs. Is each one centered on one idea, event, description, person, etc.? Are they all the same length? Ideally, the essay will have both long and short paragraphs, but don't combine or split paragraphs because they seem too short or too long.
Examine the overall structure. Are all the parts necessary? Is something missing? Does the topic change suddenly without an obvious transition? Consider rearranging paragraphs and then rewriting until the change makes sense. For transitions, make sure that the logical connections between ideas are apparent. If you write about hiking and suddenly switch to discussing the positive effects of meditation, your reader might be confused if you haven't included the detail that hiking puts you into a meditative state of mind.
Expose your vulnerability. Revealing your doubts, fears or faults can be difficult, but it will make you a more credible storyteller.
Seek to understand everything and everyone in your story. One of the main reasons to write a personal essay is to closely examine and understand what is going on. Avoid being dismissive of the motives and actions of other people. Villains are appropriate in fiction, but you will probably improve your essay by trying to see both sides of an issue. This doesn't mean you can't have an opinion -- it's also not good to be so wishy-washy that you never make a point. Readers will trust you more if your essay doesn't seem one-sided.
Avoid tidy endings. Don't try to sum up everything with a neat, storybook moral. A little ambiguity lets your readers decide for themselves.