A complete essay is like a complete puzzle.
I personally do not think about the big picture when I start an essay. I tend to type down everything in my mind when I think about the topic. It is just like when I get hundreds pieces of puzzle. Each piece of them is something in my mind at that moment. I type them down and put all pieces in front of me.
After I get all the pieces I need, I start to organize the information. Find out the main ideas in my free writing. Figure out the scene in each piece of the puzzle, and try to put together a big picture in mind.
Then, I work on the details of my essay, piece by piece. Make good connection between paragraphs.
Finally, the puzzle is complete, and I should get an amazing scene.