Determine what your child's strengths and weaknesses are and cater to them. Does he like to look at pictures or the computer monitor? In that case, he is probably a visual learner. Also, determine what subjects appeal to him. Write a list of things your child can and can't do as well as a list of subjects he likes.
Start with cards that include a word and its picture. Attempt to get the child to associate the word with the picture. If possible, show the child other examples of that item. For example, if have a word card with the word "door" on it, in addition to the picture of the door on the card, walk around the house showing him other doors. Write the word "door" on index cards with a marker and stick it to other examples of "door." It may take a while, but he should eventually make the connection that the word and the object are the same thing. If your child can speak, have him say "door" at the same time. If he can't speak, still say the word; he may start picking it up. If you child is not speaking, it would be a good idea to incorporate sign language with those items as well.
Teach action words by getting your child to perform the action. This is much more difficult than words that you can show. Make an index card with the word on it, show her the word, say the word, and then do whatever the word indicates. It will take a lot of time, patience and repetition but she should eventually catch on.
Read to your child as often as you can. This is very important. Make the reading book on a subject your child enjoys. Because autistic children tend to be very literal with no imagination, make the books nonfiction or something completely believable with pictures that show events from the story. Ask questions and have your child answer you or point to the pictures. Make the questions very easy that can be answered directly from the text with no hidden meanings.