The two Themes and Sources Essays (the Short and the Long) have a number of purposes, all directed at giving you an opportunity to consolidate your knowledge of Utopian writing. Their primary aim is to give you some experience in undertaking historical research. They will thus prepare you for a potential Part II Dissertation, and for your Part II Special Subject Long Essay. A second aim is to allow you begin to cultivate the art of constructing an argument at a more ambitious level than is consistent with a straightforward supervision essay. And a third aim is to begin to teach you the vital techniques of historical documentation: how to use footnotes to refer to primary and secondary sources; how to present a consolidated bibliography at the end of your work.
In order to smooth your path to this third goal we have provided a very short set of suggestions about presentation (PDF).
Another way of learning to present your work effectively and professionally is to imitate the practices followed in a particular journal articles (e.g. those in the Historical Journal) or in books (such as those published by Cambridge University Press). The best way of all, however, is to follow the recommendations of one of the many style manuals published by university presses and other organisations for the guidance of authors. The most famous is the Chicago Manual of Style (currently in its 14th edition), but this is a large and unwieldy treatise which may baffle as much as it enlightens. Much better for your purposes would be the style manual of the Modern Humanities Research Association: MHRA Style Book: Notes for Authors, Editors, and Writers of Theses (London: Modern Humanities Research Association, 1991). You should be able to obtain this cheaply from Heffers or online (it's listed at Blackwell's online bookshop - who ship books free within the UK - at £5.50). Our own suggestions derive in part from this little guide.
Your key concern in matters of presentation should be consistency. It matters less which lucid and informative set of conventions you follow than that they be consistent throughout the essay.