Study singers whom you admire. Singing isn't invention, it's innovation. How do your favorite performers sing? What are their signature styles? Don't think of it as copying them -- think of it as taking two or three things that they do well and expanding and combining them.
It may be beneficial to research their lives, too, in addition to their music. How did they become professional singers? What steps did they take to make it to the top? And above all, what can you learn from them?