Brainstorm about the milestone you would like to discuss. Start by writing down the milestone on a sheet of paper. Write down ideas about how this milestone came to be and how it has affected you in the present. For example, if you just finished running a 5K race, write down why you wanted to complete this goal and how it has affected you since its completion.
Write out an outline of the essay based on your brainstorm. A strong way to organize the paper would be to follow the narrative of the milestone. Begin with the reasons, or misgivings, you had regarding the goal you had such as, "When my friend, Dave, first suggested I run a 5K race, I thought he was joking". Create a beginning, middle and end for the narrative. The end of the essay should be devoted to why this event is a milestone in your life and how it has affected you.
Write the essay following the outline you created. Be sure to add in the implications of the milestone throughout the narrative. Never stray from the topic at hand but keep the sentences concise and clear.
Begin each paragraph with a topic sentence which introduces the material the paragraph will contain. Each paragraph should focus on one clear idea.
Write a bold and enticing introduction and conclusion. The introduction to the milestone essay should introduce the reader to the topic and draw them into your writing. The conclusion should quickly recap the paper but also clearly state the conclusions you have drawn from the milestone.