This isn't a game of luck. If you know some strategy and know how to throw the shot you intend, then most of this game comes down to being able to stop the power bar where you want, that takes practice.
If you move your broom to the center line, look at the rock handle to know which way the rock will curl.
If you want to change which way the rock curls, then click the button on the bottom right of the screen with the two arrows on it.
People who know these things don't say they win or lose based on luck or misfortune. You have to know what you're doing, then get good at it, that's all.