It's very simple. Keep your body as clean as possible, your mind as clear as possible. That's all you need. And do it in anyway you can, in your own way. It doesn't matter. That's why I say 'peaceful body, peaceful mind'. And then you'll be useful. You don't have to become a useful person. You will be useful.
Get better acquainted with yourself, and understand the burning ambitions that dwell within. Be brave enough to follow these. They're your dreams. Follow your dreams. They are your purpose - your purpose will fulfil you. Find it, pursue it, stop at nothing. A happier you makes a happier world.