An essay always needs a plan. Never be tempted to write ‘off the top of your head’: it won’t work. Even the most experienced essay writers plan before they write. Without a plan, an essay will be loose, vague, shapeless and full of waffle.
There are a number of ways to plan an essay. Some people like a visual or diagrammatic form, others prefer a written version. You will need to experiment to discover the method that suits you best.