The best way to promote language development for babies is simply to talk to your child. Babies learn by experiencing (and listening to) the world around them, so the more language they are exposed to the better. Additionally, you can put words to their actions. Talk to them as you would in conversation, pausing for them to respond, then you can say back what you think they might say. However, note that simply talking to them attentively is enough for them to pick up language.