Well, it depends what type of essay you want to write. If it's academic then you should develop your thesis first and choose a few key scenes to prove your claim. If it's a more casual piece (like one to post on this site) I usually focus on 3-4 main points of interest and try to blend them together in a cohesive way. Avoid lengthy introductions and conclusions, as well as any plot summary aside from what's necessary to support your point. Hope this helps :)