Enroll in an introductory music theory course at your local community college. Depending on the school's offerings, you might be able to complete an entire course of study in the field of music theory. If you're a practicing musician, try enrolling in both instrumental and theoretical courses --- this allows you to apply your new knowledge firsthand.
Converse with other musicians or music theory students. If you decide to enroll in a theory course, try to take part in study sessions or out of class meetings. These discussions help you gain a firm grasp on both elementary and more advanced aspects of music theory.
Meet with a private tutor. Many independent musicians offer one-on-one lessons in basic and advanced music theory. Search your local listings, consult with nearby music stores or inquire at your community college's music department to locate a reliable tutor. Describe your goals to the prospective tutor and work out a reasonable instruction schedule before agreeing on a pay rate.
Seek online instruction. A variety of Web-based resources are available to the budding music theorist. This option is particularly appealing to those with busy work or school schedules.