Student Exchange Programs

I am 17 years old right now and my dream was to live in the United States. I already had some experience in the United States, cuz I am a foreign exchange student right now and after 11 months in USA , its almost time for me to go back to Germany. I thought, when I finish High School in Germany , I could come back for college and then apply for being a US citizen.
I also want be a teacher and soccer coach in USA.. my dream would be to be a coach in Ford High School in Quinlan, TX, where I spend my awesome time as a exchange kid what do I have to do?, Do I have to qualify for something?, how much time does it take to apply?
PLEASE HELP :D:D:D