Start with the news that made you angry, that joke your neighbor told last week or something that has been on your mind lately. Explore your thoughts on paper or on-screen, as if you are conversing with yourself. Allow your mind to wander and make connections with seemingly unrelated information just to see where it will go. Explore. Don't worry about making sense or having a point, just let your ideas flow until they stop.
Give public meaning to your essay by discovering a universal truth within the words you wrote. Perhaps writing about the day you left your parents' home reveals a greater truth regarding some of the social and psychological dynamics of young adulthood. Maybe the day your children left home was a turning point, paving the way for an exciting new life for you that can give support to people having difficulty with the transition. Find the wider appeal and weave that into your narrative.
Avoid the temptation to edit all your mistakes out of your essay. Of course you need to write well, but admitting to naivety, errors or wilfulness at an earlier stage of life enables you to explore the experiences that helped you grow. This allows the audience to take their own meaning from your story and feel a part of it. Don't forget to be fair to everyone, including yourself. Essayist Lynn Bloom says authenticity is built upon truth and fairness, your presentation "however partisan, cannot seem vindictive or polemical."
Revision is a multi-step process that is only finished when you find yourself obsessively changing a word here and there. In reality, it is the process that started when you started weaving your universal thread through the essay to make it meaningful. Revision allows you to go back through, make sure the essay says what you want it to say (and doesn't say much of what you don't want it to say). The final stage is checking the technical details of the essay -- grammar, spelling, punctuation.