Revise your assignment, correcting errors in style and language. If you have a Writing Centre on campus, make use of their services. It can only add value to your work.
Check the spelling of any word of which you are not 100% sure in a good dictionary. Learn to use the spell-check facility on your word-processing package (ensure that it is set for British, and not for American, spelling).
Check your arguments.
Check the introduction and the conclusion.
Check your references and the bibliography.
Check that headings are consistent in size and font.
Check that illustrations are clear, that they have captions, that they are in the right place.