Write the main areas of your essay in the centre of a large sheet of paper. Brainstorm ideas connected with them, drawing lines to show how they connect and annotating the connecting lines. Add more ideas in bubbles as they occur to you drawing a flow diagram with a stage of your argument in each of a series of boxes Go back and do any of these again at any stage, especially if you feel your essay is going off the rails. Reading - because you will be clearer about what you need to find out from the texts you will have saved a considerable amount of time making your reading much more effective. Don't spend too long reading, make sure you allow time for writing the essay.
People probably learn as much from the process of writing as they do from reading.