Prepare the area that you plan to put your new divisions in before you lift the parent plant. Prune the stems and foliage to 6 inches from the ground in order to ease division and to cut down on moisture loss. Pry underneath with your tool and lift the whole clump to be divided. If the plant is very large and heavy, you may need to cut it into several pieces in place with your shovel before lifting it. This will help loosen tangled root balls and make it easier to see what you are doing.
Perennials have several different types of root systems.
Each of these needs to be treated a bit differently. Plants with spreading root systems include asters, bee balm, lamb's ear, purple cornflowers and many other common perennials. These can crowd out their own centers. Some can be invasive unless divided frequently. They can usually can be pulled apart by hand, or cut apart with shears or knife.