To encourage air to come from the lungs through the mouth, play blowing games with bubbles, balloons or pieces of tissue. Use musical instruments, windmills etc, If the child is not ready to copy you, see if he will watch you. Also see if he ever tries out things when you are not watching him.
It is always a good idea to start with things the child already finds motivating. Chances are that if you observe carefully, you will discover the things your child is interested in and will be able to find toys that are motivating. Once you have found those toys, the goal is to make playing lots of fun.