Begin with deciding your exact line of argument, and write it at the top of your page - this will be the basis for your introduction, and will then be present throughout the essay.
You should then consider the 3-4 themes or topics that you'd like to use to support your argument and make up your essay, and write them out clearly.
For each theme write out 1-2 key points/pieces of evidence that support your point, and that you'd like to expand on. If you want to make your plan very detailed you can include all pieces of evidence (such as quotes, contextual support etc) you have gathered. You may think about using the PEE (Point, Evidence, Explanation) technique to help plan your paragraph structure.
Then assess each theme and try and work out a way in which you can link each paragraph together. Find an order that works best for you, then in order from first to last find a way in which the first can link to the second, the second to the third, and so on. This way you can argue your point smoothly and clearly from one point to another.
Finally, reiterate your line of argument, and write down the final point that you'd like your reader to remember - this will be the basis for your conclusion.