Here's an edited and expanded email reply to Giovianni who is also a community member of The Organic Tango School. Giovanni owns a bandoneon but is frustrated with the learning process. This is my two-cent reply with my own advice and experience learning how to play bandoneon (and I'm still learning)... It is by no means a profession view point. Please consult many people (teachers, experienced players, etc, before you embark on your on musical studies).
As a preface to everything I'd like to say that if you're not totally in love with, and really want to play, bandoneon then nothing will really help you learn and stay with it. Fortunately for me I'm in love with both traditional tango music and Astor Piazzolla. In general, I also want to help promote highly danceable live tango music for social tango dancers with the eventual creation of many large community orchestras around the world. So everything pushes me to keep learning and practicing!
Here's the email reply to Giovanni:
Hi Giovanni, I read a great book called "Practice Makes Perfect"
Here's the actual link (http://www.essential-music-practice.com/music-practice-books.html).
If nothing else it is very inspirational to get you focused.
Also, it has many ideas/games/techniques so you don't get board.
It's hard to learn how to play bando. I do not recommend any method book. Most are for very advanced musicians and are very dry and boring (if you're a beginner). Later in your practice you can play pieces from these method books but even then it's still kind of dry. I only found one piece in one method book (Don Benito) that I use a daily warm-up.
I recommend to have fun, pick a tango song like 'Malena' (from Ben Bogart's www.TangoJam.com free lead sheets) and slowly learn the melody on the right side opening... While you're doing that, slowly learn to play the chromatic scale opening on the right. Then work on the left opening chromatic. For the left opening I also recommend learning some easy chords (G, G-, A, A-, E, E-, D, D- etc) first.
Basically, I'd have about 10 things you like to do and just do them randomly and at will so you don't get board and change your activity when you get frustrated. The best practice for me as a beginner was learning a few songs on the right hand opening. That gave me the most satisfaction.
Later, you can get more formal in your studies. However, after 1.5 years of learning, I'm still jumping around a little bit, although I have my favorite things I like to practice and try to go deeper each time... As you get more maturity in your practice you learn the difference between just playing and actually practicing. The aforementioned book "Practice Makes Perfect" explains all that.
The final thing I can recommend is to play with other musicians. No matter how bad it sounds you'll have fun. If you learn a melody or two on the right opening and if you learn most of the major minor chords on the left opening you can at least play accompaniment (chords) with a group and perhaps a line of melody here and there. That was the most satisfying experience for me. However, don't perform for dancers yet, just play with a group in private. Later, the next step, would be to play for tango dancers - that's really exciting...
If you're very lucky (as I have been) you will also run across bandoneon players in your travels or daily life who are willing and able to share with you little secrets. I have lots of admiration and thanks to give to a half dozen or so bandoneon friends and acquaintances who have given me that little bit of inspiration and advice to continue playing (and practicing)! Thanks to Adrian Jost, Korey Ireland, Ben Bogart, Christian Gerber, and to several others I've met along the journey of learning how to play the bandoneon.
Hope this helps, many hugs, Homer ;)