As you learn a style, discover what makes it unique and authentic. Play or sing it as it is normally performed, not as a stereotype. If you play the style as a caricature you reveal that you either don't know it or don't really like it, or both. How do people actually sing the blues or play those metal riffs? What is unique and excellent in this style? And all the cool things you learn will effect all your music for the better.
Even the fastest song should sound relaxed and in-control. This is about your skill level, establishing a groove, and playing in the pocket.