Charlie,
My approach is to hang the blade portion of the steel off the edge of the anvil. I use the corner of the anvil face to establish the step-down while hammering flat on the spine. It's actually easier to get a good transition on a razor than it is on a knife, which needs an even step-down on both sides.
It's very difficult to hold the blade edge up and then try to hammer in the same spot over and over to create the step-down.
Other than that, it's what Mike said--working both dimensions alternately. Make sure you're getting a high enough heat for the heavy-duty metal moving, then work at a lower temp to keep things from getting all mushy on you. :)
Josh