As a Mechanic, I have always started at the valve and in 99% of my tire repairs at the shop have never needed any assist to get the tire bead onto the rim. There are combinations of tires and wheels where you need a little assist, and in those cases I've used a Park Pro Tire lever to get things to match up.
We also INSTRUCT our customers using this same method in our Flat Tire Clinics that we have monthly. Our success rate with our customers being able to mount their own tires, tubes, on their own rims is way better that 80%. Many feel that they could never do this by themselves.
Still, on any given day there is a few flat repairs to be done, and that's easy money.