I would say, don't be afraid to use real and varied words around your child. The vocabulary you use around your child is the vocabulary he will use.
Ex. 1: Instead of always referring to the long eared thing jumping around the backyard as a bunny, sometimes call it a rabbit.
Ex. 2: Be specific - after supper, when cleaning the food mess off the kid, don't say give me your hand, say "Give me your right hand." And if the wrong hand is offered, say "No, that is your left hand. Give me your right one."
That last example can be expanded to help with many concepts: you son doesn't need to get his his shirt - it's his blue shirt; don't give him some cookies, give him three cookies, etc.
Best of luck,
--S.F.
