Before we even start writing, look at the question. See if it helps you structure the essay in any way. Does it say what areas should be discussed? For example, "Compare and contrast two totalitarian leaders and theirs economic, social and international policies"- here we already have three areas to consider, no need to think about it. If the essay title doesn't give you such help, depending on the essay, the easiest way to do it would be either to divide the essay into three sections: social, economic, international affairs/opposition or go for other main areas relevant(like leaders in Italian unification or the MAIN [militarism, alliances, internationalism, nationalism] points in world war 1). In some essays, that might be harder, as in the ones concerning unifications of Germany and Italy- here is where proper, well-organised revision should come to play. You should already have all your topics divided into sub categories before you go inot the exam room. Also remember to put in your point of argument- what are you going to be saying? For example in this topic you could state: In this essay it will be shown different the aproaches of Stalin and Hitler were. After you have that, state all the areas which are going to be discussed in your introduction. Then start every paragraph with what is going to be discussed, so with the given topic, we would say: In the economic sector, where Hitler went for rightist economic views, Stalin focused on the leftist, communist economy. Then we would go to more specified examples, like comparing public works in Germany and collectives in USSR, or the similar ideologies of self-sufficiency of both nations. You should be ending your essay with a clear conclusion, adding no more information than already present in the paragraphs.