After you have prepared your ideas and written a plan/outline, you are ready to start writing your first draft. Note the word "first". A mistake we often make is thinking that once we have written a draft, the essay is done. Not so; the first draft is only one part of the whole writing process that leads to a finished, presentable, and hopefully excellent essay. The idea of the first draft is to get the ideas out, to flesh out your answer, and to give you some content to shape and change into a finished essay. You may need to write a number of drafts in order to get to that final essay. Or, possibly, if you have really thought through your ideas and planned well, you may only need to write one draft that you then edit. It depends on what happens in the first draft - and it is best not to expect too much or too little from it.
Once you have finished your first draft
Congratulations, now you have finished your first draft.
Instead, you now have something to work with and to shape into a finished essay of high quality. But, first, give yourself a break. Leave your first draft alone for at least a few hours, or preferably for a few days. This way, when you come back to it and begin your second draft, you will have a fresh eye, more understanding of and control over your material.
When you are ready to get started on the second draft go to the How do I fix/rewrite this paper I've already written section of this website. :)