Even a simple thing as attending to and listening to your baby when they talk/babble will teach them a lot about communication. It shows respect, it shows baby how to be patient while someone is talking, it introduces turn taking when it comes to using language to communicate. Birth to three is a time for exploring - everything is new. A baby will follow your lead, so using sign language is the perfect way baby can tell you what's on their mind. Have fun with it, your baby will love you for it!