If you have multiple paper topics to choose from, pick the one that you have the most opinions on or knowledge about. This will keep your ideas flowing freely, without having to look up lots of information
Pay attention to things you have underlined or commented on in the reading. Re-reading these will remind of your first thoughts on the subject and refresh your mind. Also re-read any class notes that you have on the subject.
Make a brief outline of the paper. Make sure you jot down your most important points and have a good idea of the organization, as this will keep you on track. Write down any quotes you want to use.
Start writing. Make your introduction really good, as this is what grabs the attention of the reader. In addition, many people often feel like once they establish their paper it is hard to change things, even if they don't like the direction in which it is going.
Stick to your outline! It's easy to get disorganized and become illogical when you are pressed for time. Feel free to elaborate and include new ideas, but make sure they make sense in the structure of your paper. In addition, don't take too many breaks and make your work area pleasant but not distracting. Keep the flow going!
Write a great conclusion and final paragraphs, in order to cement your ideas and the validity of the paper in your reader's mind. Tie things together and don't create new loose ends by getting too wordy.
Proof-read and proof-read again the next day if you can. A fresh outlook will allow you to see things you missed before.
Turn in your paper and get a good grade! Make sure you have printed all the pages and a bibliography if you need one.