It's useful to think about the writing process in terms of a number of phases through which you pass. Although these phases overlap to a certain extent, you can measure your progress towards completing the essay in terms of the predominant activity involved in working on it.
In the first phase, you are still searching for an angle, or way in to writing about the question. This might involve going through as much secondary literature as you can manage, looking for a useful approach.
In the second phase, you are looking to clarify ideas that might work within the basic orientation towards the question you have adopted. At this point, looking over the notes you have taken could turn up useful material.
In the third phase, at the point when you are beginning to write the text of your essay, you are seeking to design for a reader, ie finding ways to explain to a reader the particular perspective you're taking on the problem posed by the question. The issue of how to make your text reader-friendly will be particularly important as you write the introduction, which is probably the most important single part of an essay.
In the fourth phase, when you have completed a draft of the essay, you are finding ways to improve the effectiveness of your writing. It is often useful to get feedback from a reader at this point.