Have your friend, or your mother, or your roommate read over your paper to find grammar and argumentative errors. Read your paper out loud- awkward phrases that don't strike you when you read them, often strike you when you speak them. This is a writing assignment, and you should pay attention to writing style, grammar, and spelling. Clarity is the first virtue of philosophy papers. Don't be obscure and deep- try to make your writing clear and penetrating.
Philosophy is constituted by arguments.
A good philosophy paper is one that contains original and insightful arguments. To give arguments, you must support any claims you make with reasons. Ideally, your reasons will convince me that you are right when I read your paper, but even if I am not convinced, I will be very sympathetic if I can see that you have made a concerted effort to back up your claims with argument and reason. Don't do it. Use a footnote or an end note whenever you use another person's words or ideas.