Speech threapy, give a look at "teach me to talk" podcast

Teachmetotalk.com
RDI - plenty of activities found online.
Work on motor skills
Do sensory play if child is sensory seeker
Avoid too much stimulation if child has SPD.
Love unconditionally and have a lot a lot a lot of patience.

If you haven't done it yet, get an evaluation from your state's early intervention program so your child to get speech therapy through that program.

Find a class or the book "It takes two to talk".

Some people have found the book "More than words" helpful.

Narrate events as your child goes through the day.