(I would usually take an example question such as: "'Alexander II's reforms were, on the whole unsuccessful,' discuss," and use it to explain.) So here, as with most exam essays, two main things are most important: structure and argument. First start by planning the essay. Identify what the question is asking, with this example: how effective were Alexander's reforms? Use this to formulate the structure of your essay. So in your plan, evaluate the 'pros and cons' of each reform, maybe in a table. Once you've made your mind up on each individual point, try and create a general line of argument to explain each individual conclusion you've made. It can read something like: Alexander's reforms were successful in theory, but not in practice; or: His financial and military reforms were more successful than his social and political ones. After you've created your main argument make sure every paragraph comes back to it so that you end up with an essay that is argumentative and consistent through out.