Identify your personal cognate (Crisis, Substance Abuse, Christian Counseling, etc.) and the overarching goal of that cognate (based on your learning experience-provide an appropriate citation). For example, "My area of focus (cognate) is Christian Counseling. From my studies, I think that the guiding principle of Christian Counseling is..."
If you did not have a cognate, or if you are working in a site that does not relate directly to your cognate, then you will note the guiding principle for your work at your site. "Since I will be working at a homeless shelter, I will be primarily interested in how Maslow's hierarchy of needs (reference) relates to the clients with whom I will be working." Alternately, "Working in a youth group, I will be interested in evaluating the development of interpersonal relationships from an attachment point of view."