Become so good that they can't ignore you
I like the concepts pointed out in the article linked above. The idea is to keep working at it and eventually just through sheer volume of creation and outcome of effort that you will have to produce something exceptional. Your skills will improve and your voice will be heard.
If you apply this to being a tennis coach then study, train, and keep learning while sharing your ideas.
If you apply this to becoming a better player the object is to make a systematic effort at improvement. I usually find the best way to do this is to focus on one thing and perfect it or work towards improvement.
