How do i tell my cheer coach i want to be captain?

Well I got my coach to offer it to me. I did my best in practice for 2 weeks straight. I showed leadership skills, good balance ... blah, blah, blah. And then she offered it to me. If I were you I would do the same. You should ask a whole buch of questions in cheer practice and try your very best and then if your coach doesn't offer it to you then you should ask her.