i found the go talk or something similar to work much better... i have had many different flashcards and they dont work for my son... although it may work for yours i would prefer something more structured... i just bought my son an i pad and there are many apps on it that are amazing for communication.... i like pecs and my son responds well to choice boards and first and then boards
flash cards are good. You could try matching card to card the maybe having a picture of "mum" and then matching to the person etc. You could also try using makaton signing also known as baby signing. You may also like to try a pecs board Picture exchange communication system. This is where insted of using words to communicate you use symbols or pictures and could eventually form sentences like I would like music for example.
you can try getting a gotalk i have used it for my son and its a great communicating tool...