Size up the root ball before you dig
The success of any transplanted division depends on its root system. Some divisions fail because they don't have sufficient roots to support their foliage. To avoid shortchanging plants of the roots they need to prosper, I give them a wide berth when digging them out of the ground. It's better to have more soil and roots than less. I can shake off excess dirt, but I can't paste severed roots back on.
To approximate the size of a rootball, I place the tip of my spade at the base of the plant and make a mark in the soil at the end of the spade's head. This distance, 8 to 12 inches, is usually enough to ensure that I won't dig into any valuable roots.
I pry the plant out of the ground by pushing the head of my spade straight into the ground and pulling the handle back toward me. Shallow-rooted plants come out of the ground easily, but deeper-rooted plants that have the reputation for being ornery, like large ornamental grasses, may require a bit more effort.