1. Professional Trombone/Trumpet player
In order to join an orchestra nearly always you have to attend a great music school and have at least a masters degree level. Next study with a teacher who either has experience playing in an orchestra OR has had students get placed in an orchestra. You should always go to a music school that has a great connection to an orchestra. And finally audition for as many openings as you can. There are more than three steps to this but these are the most important
2. Mathematician
I am really good at math and I love it, I can solve stuff easily after someones explained how it's done. Most of the jobs I've looked at involving math you need to have a masters degree but for some you can have a bachelors degree. Here are some steps to become a mathematician. First you should take as many mathematics courses as possible in high school, next earn a bachelors degree in mathematics to understand it. Then choose a track either theoretical or applied, and finally find a job in mathematics that you like.
Professional pianist
I have been playing piano since I was really you so this would be an easy choice for me. To be a professional piano player you will want to start at a really young age and to help performance skills you should play in as many recitals as you can. You should find a good teacher so that you can learn the best way, it also helps to have Musical talent, discipline, perseverance, creativity, and passion for piano.