To flock an artificial Christmas tree, you will need flocking powder, which is a fine, powdery substance made from ground-up foam or cellulose fibers. First, make sure the tree is free of dirt and debris by wiping it down with a damp cloth. Then, carefully sprinkle the flocking powder all over the tree, making sure to cover all the branches. Once the tree is covered, shake it gently to remove any excess powder. Finally, use a hairdryer to blow air over the tree to set the flocking powder and give it a uniform, snow-like look.