"Revising is part of writing. Few writers are so expert that they can produce what they are after on the first try. Quite often you will discover, on examining the completed work, that there are serious flaws in the arrangement of the material... Remember, it is no sign of weakness or defeat that your manuscript ends up in need of major surgery. This is a common occurrence in all writing, and among the best writers" (Strunk and White, The Elements of Style, 72).
Make sure your written assignment is clearly organized, unified, and coherent.
Are you consistent throughout the composition in your use of words, formal or informal structures, and pronouns?
Distance yourself from your writing to be more objective. You may need to take a small break. But when you return, you can have a fresh look at your work and refine it further.
Revision allows you to assess your writing from a critical standpoint in order to refine further.