Begin early. If you want to get a good grade, and more importantly write a quality term paper, do not wait until the last minute to begin your semester project. Take notes in class that will pertain to your paper. Papers that are written at the last minute are easy to spot because they lack the depth of thought and analysis that papers started early have. Even if you don't like what you are writing, begin early and get your thoughts out onto paper so they can develop.
Make sure you revise multiple times for content errors before you edit and turn your paper in. Look at your overall thesis and determine if it is developed throughout your paper. If there are superfluous sections, cut them out. Have you answered all the questions you raised? Is your argument original and thought-provoking? Also make sure you edit your paper thoroughly for surface errors so that your ideas are not competing with your mistakes in your professor's mind.
Use credible and reliable research sources in your paper. Peer reviewed journals and scholarly books are the best sources to use. Never use online sources that are not credible and refrain from using dictionaries, encyclopedias and wikis. Get a good sense of what the general consensus is on the scholarship you are working with and then insert your ideas into the conversation. Some professors want recent scholarship, so pay attention to the date of publication of your sources.
Speak to your professor about the assignment. Discuss what the term paper calls for and make sure you are both on the same page. Schedule to meet with the professor to discuss the direction of your paper. Ask relevant questions like "Is this thesis specific enough?" Does your paper seem to be interesting to the professor? Make notes of the suggestions that he gives you and consider them. Most professors will be happy to talk to you about your work. Professors want to read interesting papers and are willing to help you achieve this.