Autos really don't like to be messed with. Things like topping, defoliation, too much training can really mess with their yield. Other than, there isn't much info to go on. Have you got a decent lighting system, are they getting enough hours of light??? etc. etc.
There is a great article about growing autos in the Grow Diaries "Blog" section that will answer a lot of your questions.
Hope this helps.... Organoman.