Once you have finished the piece, you need to carefully proof and then edit it. A great paper with a lot of mistakes will not equal a great grade. After you proof the rough draft, you then have to make sure that you do not make new errors on your final draft. A little bit of proofing can go a very, very long way. If you are bad at doing this, then ask a friend to do it or hire a professional to do it for you. The cost to hire a professional to proof your paper is minimal, and you will be glad that you did it. You can find a professional by looking online.