Again we like to grow things that we can use but how do you harvest it?
Echinacea is one of the things we have growing in our garden but it's not the only root herb we have. The other one is orris root or bearded iris. I would suggest harvesting them and drying them the same way to preserve the roots for the most benefit.
Do not dig everything up at once unless you want to get rid of the entire crop. The roots will keep growing as long as you have some in the ground. Personally I like to keep 3/4 of the plant still planted so they will keep producing more roots.
When drying it's best to let them air dry for some time. I recomment drying orris root for several weeks in the sun. but if you're in a hurry you can always use a dehydrator. When it's dry you can crush it up in a morter orspice grinder.