"A thesis is a claim that is provable (i.e., can be backed up by evidence of some sort), not obvious (i.e., something that others could disagree with), and engaging enough to sustain your reader's attention (and your own interest!) for a 10-12 page paper...
'Within Our Gates is a powerful example of a counter-history of race relations in this country. With his film, Oscar Micheaux set out to combat white supremacist histories of race relations in the United States, such as that conveyed in D.W. Griffith's Birth of a Nation(1915), but he did so by re-purposing the very representations that were used in those racist histories. In this way, Micheaux furnishes one of the first instances of a film director as a re-mixer.'
While certainly not perfect, the second example is at once more specific (i.e., not immediately apparent or obvious) and, as a result, engaging than the first. This is the kind of thing you'll want to aim for in making your larger claim.
Making Your Argument:
Of course, that a thesis is provable assumes there is actual compelling evidence for doing so. To this end, your paper should draw upon the following: