Be what God intended for you to be. For those who would rather not put it that way, then here is another way to say it. Discover your gifts, find what you're good at and what you enjoy doing. What are you passionate about? Develop those gifts. Because you are gifted in that way, for the same effort, you will be better at it than one who is not gifted in that way. In other words, you will have a greater return for your efforts.
Now if you are exceptionally gifted and society does not have a nice little niche for you, then you may just have to carve out a niche for yourself. But until you have the resources to carve that niche, you may have to work at something you're not so passionate about. That's OK. If God intended a path for you, walk in faith and you will get to your destination.
Please don't just "be whatever you want to be." Be what God intends you to be.