The best advice is to apply for aid at every school. Check out the availability of fellowships, assistantships, etc. The best sources of information are the financial aid offices at the schools to which you are applying.    

Fellowships may be based on financial need and/or academic merit and are granted by universities, private foundations and government agencies. Some universities will waive tuition for fellowship holders. Often there is a 9-12 month stipend, sometimes tax-free. Some of these are for one year and some are renewable.

Traineeships are awards from outside agencies usually administered by graduate programs. The traineeship may or may not involve experience outside of academic work. Assistantships (typically teaching, lab and research assistants) are granted on the basis of need and qualifications.    

Other places to look are your undergraduate office of financial aid, your undergraduate department, etc. Also look for state scholarships, to your parents' companies for possible awards, and awards available to minorities, women, children of veterans and children whose parents are deceased. Check with community organizations such as Elks and Rotary.    

Many students take on a job while in graduate school, but only as a last resort. Work, even part-time, is difficult and exhausting with the kind of study schedule you are sure to have. Departments prefer your work be limited to the lab or research type. You may find your institution is willing to work very hard to help you find work directly related to your study if you must work at all.

Financial aid web sites