A recent study by a British
group heard on NPR
(1) essay grades are very subjective. (Of course.)
(2) grades correlate primarily with style, not content.
The brilliant college freshman who writes his heart out in the first person will get a lower grade than the dimwitted sophomore who has nevertheless mastered the art of the academic writing style.
Some basic techniques might be to use the passive voice, familiarize yourself with the jargon of your field, avoid mention of yourself (especially in the first person), and generally wring out your writing until it is as dry as possible. Never address the reader as "you" in your paper--in fact, don't address them at all. Just state facts. Eliminating the personal is key; the more you show of yourself the more vulnerable you are to attack. This alone, no matter how bad your thesis, will increase your chances of getting an A.