How to become a pharmacy tech in stores like Walgreens, CVS, etc.?

I'd like to know how to become a pharmacy tech in stores such as Walgreens, CVS, etc.? I'm interested in persuing a pharmacy career. I've been volunteering in my hospital for 2-3 years in the pharmacy department and in other locations around the hospital. I have a good/decent gpa with honors. I've never applied to a job before, so what would be the ways to increase my changes in getting hired? And do I need to be certified? I'm 18 and I'm a high school graduate. I'm thinking of applying full time then applying part time when I go to college.