Applied Behaviour Analysis (ABA) is a proven method to improve development progress in children with autism. It is more therapist-focussed, systematic and well-structured with lots of data gathering. Although it is believed to be effective and well recognised by stake holders of autism, it has been criticised for 'making a robot out of a child'. As a result another therapy method called Floortime came to being. Unlike ABA, Floortime is more child-centred. While the child takes the lead the therapist follows and engages with the child through fun and excitement.
Now we have Relationship Development Intervention (RDI). It is more focussed on improving interaction with the child through joint activities. If you wish to know more about this approach log onto http://www.rdiconnect.com/
Here are some videos http://www.rdiconnect.com/video/default.asp
On the left I've also included a link to a good website. There you can see how RDI is implemented by the parents as a lifestyle to encourage the child to interaction and respond more to them.
Please note that I do not imply that RDI is better than ABA or Floortime approach. For a good result I advise parents to use a combination of them while keeping in mind each child is different and a method which had worked on another child might not work for your child.