heres an exercise for intermediate players.
take a easy major scale c or g major.put yourself into 6/8 time.
go up the scale playing two semi quavers and two quavers using cross fingering cc c c, then practice it with the two semiquavers in the middle;c cc c       again using first and second fingers or second and third fingers,your count will be 1and 2 3 , or 1 2and 3, use a metrognome slowly at first, 90 then build up to jig speed 116[approx].DickMiles [ concise english concertina tutor].