I worked at my uncle's bicycle shop while in highschool. At first, I primarily stayed in the back working on bikes, cleaning, or restocking tubes on the floor. As I got interested in the sport, I started helping customers more - first with on-the-spot repairs then, eventually, selling bikes. I stutter a lot less when I'm talking about something I'm interested in and I know about. Not that I never stuttered in front of customers, it just wasn't as often and I had a routine. The worst was calling customers on the phone, though. I recommend, if you can, trying to find a job in something your interested in.