How do writers develop ideas for writing? Writers use many techniques, and it's a bet that most of the techniques involve writing itself. Think of a composer creating ideas for a song by playing notes on a piano keyboard. Think of a sculptor creating ideas for a statue by shaping and reshaping pieces of clay. Think of a quilter creating ideas for a quilt pattern by arranging and rearranging different snippets of fabric. All creative endeavors go through preliminary stages in which creators generate ideas, discard some, and play with others that capture their imaginations or that seem to "fit the bill." Each creator develops ideas by getting immersed and "doodling" in the particular medium. And writing is no different. In writer's terms, that preliminary stage of idea development is called "prewriting."
Prewriting usually is messy in terms of having ideas scattered all over the place--think of the quilter with pieces of fabric all over the living room floor. For a lot of people, it's liberating to be messy and not worry about logic, pattern, or final form. That's the purpose of prewriting, to be as free-ranging as possible in generating ideas. If you're aggravated by mess, then prewriting can be thought of as pre-planning, as a means of generating the ideas and data that will help you create the essay draft. Either way, prewriting is a stage of idea incubation, a way to generate ideas and capture your thoughts through writing.
Ideas for writing develop in many ways, and prewriting techniques try to reflect the different ways in which ideas can develop. Some forms of prewriting are intended to help you bring subconscious ideas and interests into consciousness (some forms help if you tend to draw a blank when you're asked to "write about what interests you"):
Other forms of prewriting are intended to help you generate your own ideas in response to others' ideas:
Still other forms of prewriting are intended to help you both generate and focus ideas about a subject that you've already chosen: