Print multiple heads to test matching paint colors and trying multiple version of textures and materials.
Use the dry brush technique to paint the hair.
Use a fine point, like a tooth pick or needle, to carefully add the eyes and brows.
Match figure textures
You can also use the dry brush method to match textures that are part of the figure, like the moss on Groot's body.
Clean the socket inside the head of any overhang filament. Press fit the head onto the ball joint!