1. Talk to him constantly. Tell him everything you are doing as you help him dress (name type and color of clothes as you put them on him, talk about buttons and zippers like count them, etc.), as you walk around the house or a store -- always have this conversation going with him.
2. Read those web sites for parenting helps.
3. Find sites for children's finger plays and songs and stories. Do those with him.
4. Never make fun of him or criticize him or try to hurry him.
5. Try some of these ideas --
Activities to Encourage Speech and Language Development
6. Try to get him to look at you. I'm betting eye contact is not good. Make it fun, like a game, Peekaboo etc.