While reading this, please remember, I applied, and was hired, seven years ago, before the recession. Some of this may not apply anymore.
I applied online (as there are no paper applications for this company) on a Sunday night, and got called the next morning. One of the main things they look for in applications is previous animal experience, prefferably professional, not just at home. I had worked at a dog kennel and several animal clinics before applying here, so that helped in the speed with which I was called for an inerview, I'm sure.
The interview was nothing special. Nothing above and beyond a typical retail interview. Obviously questions about my experience with animals. Where I hoped to go in the company. My work attitude and ethics. What had happened at previous jobs (why I quit, or was fired, etc).
I started at Petco in Florida. At least there, they required a drug test after the interview. As far as I know here, they do not.
At the time, since the recession had not hit, Petco generally tried to compete with whatever major retailer they were next to in regards to starting pay. A lot of Petcos are near Targets, and at the time Target was paying $9.50. So that's what I was started out at. But now, as far as I know, everyone is started out at minimum wage (except the few people who are hired from outside the company into management directly).