It’s as well to keep in mind what you should not be doing. Do not introduce lots of fresh evidence at this stage, though you can certainly introduce the odd extra fact that clinches your case. Nor should you go on to the ‘next’ issue. If your question is about Hitler coming to power, you should not end by giving a summary of what he did once in power. Such an irrelevant ending will fail to win marks. Remember the point about answering ‘nothing but the question’? On the other hand, it may be that some of the things Hitler did after coming to power shed valuable light on why he came to power in the first place. If you can argue this convincingly, all well and good; but don’t expect the examiner to puzzle out relevance. Examiners are not expected to think; you must make your material explicitly relevant.
Here is another example of a simple error of omission that could have been caught if the student had read the essay aloud or given it to a friend to read. The word "of" should be between "calculation" and "the." That one small error makes the entire sentence awkward and confusing. If the instructor has to reread the sentence to try to understand its meaning, the flow of the essay is interrupted. If this happens often enough in the essay, it gives an overall bad impression on what otherwise might be a very good paper in terms of research.