Great helpful video about how to prune a holly bush. Here are some tips:
Prune in December. It is good for the tree, and you can use your cuttings to decorate for the holidays around your house.
Avoid shaping your holly too much. You shouldn’t expect holly to be a boxed hedging or topiary. Prune the bush in a way that continues the natural growing shape of the plant.
Start from the inside and work your way out. Cut away branches that are rubbing on each other or any branch that looks diseased or dead. Trim branches just above a new leaf bud or all the way back to a main branch. You can cut a great deal off of your holly to thin it out. Doing this will make your bush full and lovely again in a few years.
Avoid using hedge trimmers. Taking the ends off branches and leaves doesn’t help your holly grow and creates an unappealing boxy look.
Remove all the trimmings. Salvage some for decorations around the house but dispose of others. If any are diseased, keep them away from your holly bush.