Hello everyone. I know I haven't been online in ages, hopefully now I'll be able to return to my old habits on here Anyway I was hoping someone would be able to tell me when and how I am to prune or cut back my Purple Leaf Sandcherry tree. I just found out that it is a tree that needs to be pruned every year but I don't know when or how. Any Suggestions?
Plant Faerie

It is best to wait until fall, that way you will not be having insects target in on the open wounds and vectoring in diseases.
You do not have to prune it heavily each year, but pruning does help encourage new growth, and will help thicken it up. When making any cuts, be sure to prune all the way back to the branch collar. This is the round swollen area that kinda resembles a toilet seat that the branch comes out of. Prune as close to even to the face of the collar as possible.

1st thing is to remove any sucker growth (the branches which appear to grow straight up from the trunk or branches.
2nd you can remove any lower branches which make mowing a hindrance, then the rest is pretty much up to you and how you want to shape the tree.
Just remember you can always go back and cut again, but once cut, glue does not work too well to fix any mistakes