You should make sure the professor knows who you are. Participate and ask questions in class, show up on time, and visit the professor during office hours BEFORE you ask for the recommendation.
When asking for the recommendation, it may be a good idea to provide them with a brief statement of purpose. You can use a version of the essay from the application. They will appreciate this because it helps them to know where you are coming from, why you want to study away, as well as how studying abroad fits into your academic and career goals. We recommend that you email them a link to the program website in case the faculty member has questions about the program.
Make sure to communicate with your faculty recommender regularly. Provide them with ample time to complete the application prior to the deadline. As the deadline approaches, be sure to touch base with them as they may have forgotten or lost the email. Be realistic when asking a faculty member; if it is the week of the application deadline or even closer, ask if they think they will be able to complete the recommendation on time.