I signed up with Kelly services, way back in the day, looking for my first job.
They took three weeks to get back to me, and so in the meantime I had been filling out applications everywhere else and had already been hired and was about to get my first paycheck. At McD's. I had decided I'd rather do hard work in a polo shirt than wear a skirt and sit all day. But I was 16, I drive a desk now.
I haven't known all that many people that used temp agencies, but it sounds like you have to sort of build a reputation for reliability by taking any shit job they throw at you and never call in sick. Starts out sporadic, but you can get placed pretty decently after you'd been at it for a while.
But for that degree of working your way up, I highly recommend taking any entry level job with a union you can find. Because then you have regularly scheduled pay raises and it gets much better really fast after the first year. Get your toe in the door and take all the educational courses they will offer you to work your way up a few levels.
Good luck!