I am a great fan of the Online Academy of Irish Music. Edel Fox, Ernestine Healy, and Liam O'brien teach a series of lessons designed to systematically build on each other. I have an extraordinary teacher as well, and far from being insulted that I am bringing extra information into our lessons, we use the stuff I am learning on OAIM as a springboard to tweak things, as well as bringing up repertoire we might not have thought of. I highly recommend it.
I also want to second the suggestion of playing as quietly as your concertina will allow for at least part of every practice session. As a beginner I was guilty of one volume practicing to the point of making my ears hurt. My teacher looked at me during one lesson and said, "Play like you're trying not to wake up the babies." I do that consciously every session and it makes me so much more aware of what is going on in my body as well as the music.