here is what Alatair Anderson wrote in his tutor.start with the bellows a little way open,then while playing the notes extend the bellows steadily until they are fully open.Just before you run out of air ,change direction and steadily close the bellows until nearly shut,then open them again.
this is how I play too.
one fault some English concertinsts make,is to not articulate or keep seperate each note,but to run one note in to another,personally I think seperation is important on tunes http://www.dickmiles.com