First, completely cover your bauble shapes in white paint. To get a full, even covering, you will probably need to apply at least two coats.
Once your shapes are dry, draw your bauble designs onto the front of each shape using pencil. Once you are happy, go over your designs using a black pen. For little details, use a finer pen.
Try mixing words with simple geometric designs for a beautiful variety that will look very striking on your Christmas tree.