To help teach wet and dry, create a more vivid experience for your child. Have a wet face towel and a dry face towel, for your baby to feel and experience the sensations of wetness and dryness, and the contrast between the two sensations.
Contrast dry and wet using the respective flash cards to help your baby learn these two words. Once your baby understands these basic concepts, you can do extension work by asking whether various things are wet or dry. "Is water wet? Is water dry?"
Get all four volumes of Baby Signing Time...