The best way to write an essay describing a life experience is to use either a personal or narrative essay format. Although they're very similar, there are some slight differences between personal and narrative essays. A personal essay is a reflection on the impact that a significant event has had on a person's life. A narrative essay is the conveyance of that same life experience in story-like format. The chosen format should reflect the author's goal.
College essays are a great example of the personal essay. The objective is typically for the author to convey to college admission officer the significant event or events in one's life that led an individual to apply to a specific college or pursue a particular field of study. Readers of personal essays are looking for logic, reasoning and connection from point A, being the significant event, to point B, being the college application. In many ways, a personal essay is an analysis. The personal essay typically follows the common essay format of an introductory paragraph, body of supporting paragraphs and a conclusion. The event in question and its impact should be clearly stated in the opening paragraph. A narrative essay is much more free form in nature. It is much more like telling the story of the event and does not necessarily call for reflection, though it still should make a clear point.