Lips

During a song you will earn star power by singing well. To activate that star power you will have to perform an action by moving the microphone a certain way as indicated by an animation that comes up on the screen. Once the star power is activated you will earn stars for singing well for the duration of the star power. This achievement will unlock once you have earned 5,000 stars across all songs you have sung.

You can earn the star power quicker by shaking the microphone to make percussion noises, but that can become very irritating and tiresome, so I suggest just enjoying the songs and letting this achievement come naturally from playing the game.