I've tried to think how to write this post for a while but have stopped because my language skills probably will not be sufficient, but then I thought I should try something new so I used Google translate and then I adjusted the english text a bit.
So here it goes, some advice on learning after a bad start. Best is of course to avoid the bad start, but if you realise you need a change early you can make the change now and then you will not loose all those following important years. These is things I think I had benefited from if I had known this when I started and if I had understood a post like this one and if I had been able to make my mother and father understand so they did something about it. They could then have helped me to get another teacher since I become so interested and practiced a lot. That had probably made a difference
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I have been struggling to repair a bad start since I realized myself that I had developed in a way that I had reached a dead end. Teachers might have seen it before I did but they didn't say anything. In the mirror it might be because they didn't know how to deal with it. The turning point first came when I was 17-18 years old when a new teacher was straight and told me so, so I understood how important it was to fix my technique. Now it is more than 40 years since I started that technical journey.
About my journey
Started playing trombone in 1975 when I was 12 years old and then quickly learned to reach an acceptable level so I could start to develop note reading and deepen my interest in music. My bad start was only about four years of having a teacher that could not play trombone or any brass but those four years cost me another forty years to fix and probably it also cost me a better musical career. In 1980-81 I made that drastic change to the emboschure and the slide technique, which meant that I had to start all over again for six months and then could not play at all. I had to relearn away from a terrible smile emboushure. It raised me a level and in 1983 I entered the university on trombone. My technique was not fully repaired so I could not absorb the teaching there very well because it made high demands that the technique should be fully developed. I struggled with the concerts I had to play with that insufficient technique and had no real idea how to follow that transition from smile emboushure to "puckered". A got another teacher at that college and he only concentrated teaching on concerts which I was not ready for. Musical confidence got low and I hid behind those who were doing everything right. After finishing my studies, I started to decide for myself how I should change my practice and gradually with maturity I learned to be my own best teacher. Here, then, the development curve began to change from being a linear rather flat curve to an exponential curve.
What has happened in the last maybe 10 years is that the slope now rises very steeply, so finally I can fully go up and concentrate on the music when I play. I no longer have the mental blocks that were nurtured and inherited from my bad start and shaky followup. Now since ten years everything feels very good to play and my technique feels solid. It's now just a matter of strengthening and training further to fine tune everything. Those small corrections now makes me take leaps in playing. Music is now very fun.
Some concrete technical advice how to overcome problems I leave to teachers but I want to give some general advice that has nothing to do with concrete technical advice and that is to take advantage of all the opportunities offered when musicians you admire and play with give you all those "free advice" in person, because it is based of what they see and hear in the moment and often is very sincere. If you are in training then instead listen to your teachers, but then make sure that you really have a good teacher who is not only a nice teacher but someone who has solved the puzzle, who knows what the path to learning to a high level means. Ask all kinds of questions to those who give you information so you really understand. Don't leave those important moments in confusion. Don't forget that what is most important is being able to translate that information into something fruitful when you get home to practice. Practice smart. All that important work you have to do yourself, because then you are alone. Always think about what the information you pick up means to just YOU in each situation. The earlier you start to take great responsibility for your learning the better for your learning curve. This is what I believe. It's a bit late for me to try to pick up competition to get a full pro career now then I'm in my late 50ies so it will never happen, but to be able to do music at an always higher level then the day before is what I want as my award.
/Tom