Make sure you understand what's expected. According to award-winning composition professor Richard Fulkerson, teachers approach writing assignments from some combination of four main objectives or purposes--expressive, mimetic, rhetorical or formalist. Knowing which one to use will dramatically improve your grade. Don't worry; you don't need to know all the details to figure this out. Simply ask yourself (or your teacher) if he is expecting evidence of personal growth, if he wants to assess your technical writing ability or if he hopes you produce something that will inspire or convince an audience. The answer will help you narrow your topic and focus the essay in the expected direction.
Narrow your selections to a single accomplishment. If you've done something incredible, this will be an easy step. If you can think of many accomplishments you're proud of, it may take a bit more time. Reduce your list by carefully considering each item. Will it be a struggle to come up with enough details to fill out the paper? Will it meet the expected purpose or objective of the assignment?
Select the main points you want to make. You need at least three points to discuss in your essay while also focusing on the expected objective for the writing assignment. If the teacher wants personal growth, determine ways that your accomplishment changed you or taught you valuable lessons. To inspire, you'll want to focus on the extent your accomplishment influenced others. Prove your accomplishment is something to be proud of to create a convincing argument. If the teacher is trying to determine your ability to follow the rules of writing, you can take any of these approaches as long as you make sure the final paper has the correct elements included.
Fill in the details. Every student has a process that works best for them. This can range from free-writing to thought bubbles to formal outlines. What you want to do at this stage is to give yourself plenty of material to work with, so write down as many ideas as you can that would help to support each one of your main points.
Pull your ideas into the formal elements of a paper. Do this by writing your accomplishment and your purpose into a thesis statement sentence. Make a topic sentence out of each main point and write each supporting idea into sentences. Organize the paragraphs in logical sequence, add an introduction that talks about what your accomplishment was and a conclusion that sums it all up.
Revise, revisit and revise again until you are satisfied.