Not sure where you live, but if you haven't checked into any of the Early Intervention programs you should, as these are a tremendous help, especially the earlier they are started. At age 3 they are actually able to start Special Education Pre-K though the school system as well (if I remember correctly).
As to things you can do with your child to help them - using a Picture System (like PECS) to label everything, and then constantly repeat names of thing and point to the pics. Early reading books with lots of pictures, where you can sit with them and name the things in the books. Baby Bumblebee has a video series (primarily geared for infants), that uses phonics and other early learning techniques that they can watch.
In the end though, a lot will depend on where your child is on the "spectrum", as to when he will start talking (or if he will ever do so). My son is 10 and while we know he is trying desperately to talk, he never gets more than an occasional word out, most of the time it is simply vocalizations. It can be heartbreaking, but we definitely don't give up hope. Also, just because they can't talk, doesn't mean that they don't/can't develop other means of communication.
Start off with 3 simple words it may take a month or two.When he/she shows some sort of progress no matter how small,reward them and show how happy you are that they're trying.I've heard parents try,from tv shows to computers to even writing as a form of communicating.It's a 50/50 shot and it can't hurt anything.Good luck,hopes this helps.