Befriend someone in the registrar’s office.
An inside contact can place you at the top of a waitlist, determine the likelihood of getting into a particular class, give you information about the professor, or even slip you statistics on the dropout rate of the class.

Ask the professor in person.
Make the extra effort to plead your case directly. Seek out the professor during her office hours before the first class.

Present a compelling reason.
Earnestly convey a specific reason as to why you are so keen on taking this particular class. Mention that you’ve already done a lot of work in the area of study, refer to an obscure article, or say that you’ve published articles on the subject. Convince the professor that your experience and enthusiasm will make the class better for all students.

Flatter the professor’s curriculum vitae.
Bring up a few details about the professor’s alma mater, publications, academic expertise, and reputation. Demonstrate that you are an admirer who wants to study at the feet of the master.

Attend the first class.
See if someone drops it or if there are unexpected openings. Stay for the whole class, and participate. Make your presence known. Have all necessary paperwork on hand in case the professor agrees to admit you to the class.

Be persistent.
Go to the professor’s office. Leave her numerous voicemail messages. Visit her office again. Keep yourself in her field of vision—she may give in and admit you, just so you will leave her alone.

Cry.
Crying may help you gain sympathy.