Become an AZPOST General Instructor, (40 hr school) become an AZPOST Firearms Instructor (80 hr school). Patrol rifle is a separate 40 hr block. Satisfy all your agency's suckup or performance standards along the way.
As far as shooting skills go, POST requires 210/250 to be a cop. I think it's 235 on two shoots to get into school, and yes we've sent people home from the instructor's course, both on academics and on the quals. My agency has instructors shoot 240 to stay on the roster. I was an NRA instructor before I applied, it was one of the things that helped in deciding who went to school...more applicants than slots.
"To spit on your hands and lower the pike; to stand fast over the body of Leonidas the King; to be rear guard at Kunu-Ri; to stand and be still to the Birkenhead Drill; these are not rational acts. They are often merely necessary." Pournelle