Secure a scholarship: Graduate programs typically award scholarships and fellowships based on merit. It's going to vary from school to school and where that particular student sits in that applicant pool.
At many schools, aid is given out by academic departments or the specific graduate school instead of a central financial aid office, so you may have to do some digging. A graduate admissions official or someone affiliated with your desired program can help you sort through the options. Experts advise applying for funds as early as possible to ensure access to the full pot.
A range of private and public organizations also offer money for graduate school, though these fellowships are typically highly competitive. The Truman Scholarship Foundation, for instance, annually awards up to $30,000 to each of about 60 prospective grad students looking at public service fields. Both Cornell University and the University of California-Los Angeles provide comprehensive online databases of awards across a range of fields.