I would also strongly advise you not to make an essay based upon the lines of arguments for and against (i.e. the old fashioned GCSE, everyone's view must be considered pap).
After having looked at the historical question in general, both at previous historian's opinions and also the recognised facts, I come up with a general answer that I personally believe in. Sometimes it is unique, sometimes it is simply to agree with a previous historian.
Then based upon that I start to structure different answers about the same topic. Sometimes its nice and essay, for instance on the role of the individual in an event. Individual's influence vs. circumstance. Or sometimes it can be more complex, so for instance 'Assess Bismarck's role in the unification of Germany' (Oxford submitted work, and thereby the one in which I've found the most ways of perfecting, all in the one week post submittion itself).
I argued that for every circumstance that was critical to German unifcation, Bismarck made use of the relevant circumstance, and that resulted in the actual event itself.
So essentially, summarise your argument in the introduction and declare what it is that you intend to prove. Then in each paragraph cover a different factor, and at the end of each paragraph conclude on how it helps to answer your question. In the conclusion you should be able to draw upon each mini-conclusion made at the end of each paragraph to make your overall answer to the question.
At least, thats how I do it. Or, at least, thats my general aim of how to do it. It rarely actually happens, but hey.