Compile all the knowledge and research you already have on the topic. You may surprise yourself at exactly how much you already know on the subject, and you'll quickly see exactly which topics you need to do more research on.
Write as much of the paper as you can with the research you already have in front of you. If you come to a section in the paper where you need to explain something more in depth but you don't yet have the facts to back it up, make a note of it within the text of your paper and come back to it later. Write everything from the introduction to the conclusion as well as you can.
Read through your paper and write down the facts and information for which you need to find sources. Also take note of any source requirements listed by your professor that you don't yet have. Find sources that have the information you need and that fit the source requirements set out by your professor.
Add the new information that you have found into the sections of your paper that need more research. As you add facts, be sure to document them within the paper to reflect where you found the information to avoid plagiarism. Flesh out all the arguments you make supporting the claim you make in the thesis of the paper and don't leave any questions unanswered.
Read through your paper again and make edits and revisions. Depending on the new information you found and added, you may need to rearrange elements of your paper to make the paper flow better. Double-check for proper spelling and grammar. Continue reading the paper through and making revisions until you see no more mistakes.
Create the formal citations of all your sources and add them to a "Works Cited" page at the end of your paper. Depending on the preferences of your professor, you'll either need to create the citations according to APA, MLA or Chicago style formatting.
Give your paper one final look-over about an hour before you hand it in. Ideally, you'll have finished the paper at least an hour or two before this and you'll have given your brain some time to rest and refresh. Make any more changes you think will add to the flow of the paper. Print out a final copy and hand it in.