Okay, this does not mean being cutthroat and mean and going around torturing people and stuff. This means, be ruthless when it comes to your material and your standards. Experiment and see what genre you are most effective and sound best at, and when you find it, drive yourself to master it and to continually evolve as a musician. Be honest with yourself. Do you sound good singing in this particular style? Are you even interested in the genre that you are singing? This counts. You should enjoy what you’re doing, because it would be heard and felt in your music.