Alexander Technique
Further to a number of references to the Alexander Technique - I am a great fan of this and can truly say it saved my career. I had three years of quasi weekly lessons and can report that I was able to incorporate it into my own flute teaching. What took me so long to undo modifies my students' approach to playing almost overnight - not a question of my skill, but that things are so much less ingrained at college age. Alexander study is like flute study. A good teacher makes you aware of something about your playing and you end the lesson playing better - but after a few hours/days you forget the feeling/sound and need another lesson to recapture it - and so on until it becomes a part of you.
It is also like psycho-therapy in that you have to peel away one level of problem to reach another - again, the younger you are the easier it is. However, just as in flute teachers and therapists, the benefits do start with the first lesson (or find another teacher!)
With my teacher I worked on the flute for half of each hourly lesson (after basic posture/movement work) and truly believe this is what made the difference. My previous experiences with other "isms" had led to good behaviour modification but not when I played. My teacher, who was a clarinettist, was able to instantly perceive all my tensions - in fact, in lesson one, after she said "OK let's go to the flute" she said "did you know that the moment I said the word flute you tightened up", and later, "the moment you put the flute to your lips....” She was actually the best flute teacher I ever had. - start young!