You can create bleeding art from tissue paper in a couple of different ways. As you place small strips of tissue paper down, you can either wet a paint brush with water and wet the strip that way, or you can wet the strip by spraying it. Both methods work well.
A fun tip is to draw a design with a white crayon then place down the tissue paper. When you lift the tissue paper up, you will see your design outlined! Another helpful hint: thicker paper, such as cartridge paper, absorbs the dye better than thin printer paper.