Establish eye contact with your child/client- if this doesn't come easily for your child/client try bringing items to your face before you give it to him to draw his eyes to yours.
Sit at your child's/clients level- Get in the floor, on your knees, or in a chair when he's in his high chair. This should also help with eye contact.
Follow your child's/client’s lead- If your child/client is interacting with you in anyway, the best thing you can do is to KEEP THE CONVERSATION or INTERACTION going, regardless of your original "plan."
Provide choices for your child/client- This way you're teaching vocabulary ("milk or juice?") and giving the child/client some bit of control in the situation ("puzzle or ball?")
Take turns with your child/client- That's what we do in a conversation, we take turns. You can make anything into a turn taking game. This will aid in social skill development and the words "my turn."
Imitate what your child/client says and does- This should encourage them to imitate you. Actions are easier than verbalizations.
Wait expectantly for your child to respond- Some children need more time to process and respond. When you prompt for an action, sound, or word...stop, wait...then repeat it. And don't dismiss communicative attempts. Interpret your child's/clients nonverbal actions and speech attempts- If your child/client is only pointing or gesturing, put a word or sound to their gesture. Teach them. Talk about what you're doing as you're doing it. Praise all efforts.
Be childlike and animated- Be fun, be loud, be quiet, be animated, be loving, be affectionate, be silly.
Label and describe things in your environment.