You are unlikely to get better simply by following a protocol or retraining template.
You must take charge of your own situation. Getting advice from others is important, but not as important as creating your own path for improvement. Try all the strategies you can but be open to modifying them so they are most effective for your unique situation.
The most effective retraining strategies require having the instrument on your face.
Exercises away from the instrument can be helpful in alleviating tension and setting the stage for success, but to create a new habit, you must be in the act of actually playing.
Extrapolate ideas from others who have had success, even if they don’t play your instrument.
Be clever about adapting strategies that have helped others and find ways to apply them. For example, David Leisner suggests using large muscle groups instead of micro-managing the small ones. As a brass player, you could interpret that as meaning the embouchure is more than just the orbicularis oris – it’s also the masseters and buccinators, etc.
Do not try to play in public while you retrain.
When you play for others in any capacity, you will revert to your old way of playing and deepen the aberrant neural pathway in your brain. That’s the last thing you want to do because it will make it that much harder to create the new neural pathway. If you have a full-time playing gig, you will need to take a sabbatical from your playing commitments. It took me about two years to retrain to the point that I was comfortable playing in front of other people. If you teach, do not try to demonstrate for your students. If you think you will be tempted to pick up the horn as you are teaching (and you probably will), leave your instrument at home.
If you are depressed, get some psychiatric help to work through the depression.
There is no shame in seeking this kind of help. I did and it paved the way for all the other strategies because I was able to more clearly view the situation objectively. It’s perfectly natural to feel depressed, but don’t let the emotion control your future.
Take stock of your situation.
Musicians with dystonia can lack healthy perspective. When I was initially diagnosed, I was very depressed until I took a good look around and saw my beautiful wife and children and was able to realize that playing trombone does not define who I am as a person. Once this revelation sank in, retraining became much easier for me psychologically. Ironically, I also became a better father and husband.
Keep a journal.
Use the journal to record your successes, failures, and frustrations; I was able to cultivate some of my best ideas this way. You don’t have to show it to anybody if you don’t want to.
Learn as much as you can about dystonia and neuroplasticity.
Start by reading from the list of Retraining Resources on this website.
Seek help from knowledgeable musicians.
Not all musicians are truly knowledgeable about dystonia (in fact, very few are). Seek help from those who have been through it and who have genuine expertise.
Take Alexander Technique lessons.
Taking Alexander Technique lessons awakened my dormant kinesthesia and helped me discern tension in my body. Those who have played with tension for any length of time need the help of a trained movement therapist to help them discriminate the quality of their effort while playing. The patterns of tension and aberrant movements are quite durable and habitual, and Alexander teachers are trained to help you distinguish them.
Take Feldenkrais lessons.
Like the Alexander Technique, Feldenkrais is designed to help you rediscover how to move your body free of tension. The two therapies deliver the same sort of message in different ways.
Do some Body Mapping.
Your body map is your internal representation of how your body is constructed and how it is designed to move. If your body map is inaccurate, your movements will be awkward and potentially injury-producing. Refine your body map to ensure you are moving with ease as you make music.
Do some yoga.
Yoga encourages movement experimentation and is widely available. Take care not to confuse the breathing recommended during yoga with the breathing needed to play a brass instrument.
Cultivate global awareness.
It’s human nature to concentrate exclusively on the part of the body that is not cooperating. Doing this will almost certainly make the problem worse (it did for me). Instead, learn to spread your awareness out to include your entire body, your surroundings, and all the sensations you are feeling.
Do some constructive rest.
Constructive rest is a way to bring your body to as much muscular freedom as possible, refine your body map, and cultivate global awareness.
Connect the dots.
It’s critical to understand that a movement therapist (such as an Alexander teacher) may not treat the dystonia directly, but the global work they do will provide the foundation upon which you can actively create a new way to play. Make meaningful connections in your thinking about this issue so you understand clearly how the movement therapies can help you.
Don’t try to recapture the past; instead, redefine the future.
I tried watching old footage of me playing before I had dystonia to rediscover how I had been successful. This did not work for me. Instead, I left the old way of playing behind and reinvented myself as a different player altogether.
Rethink your approach to music making.
For me, redefining the embouchure and taking a non-athletic approach to trombone playing were important keys to retraining. The more well defined your new approach, the better. Think through the differences between your old way of playing and your new way and articulate them clearly by writing them down, discussing them with other musicians, and reinforcing them over and over.