The very first factor for success of a song or a piece of music is courage and confidence.Without confidence of oneself,he can never do anything well.As well,confidence makes healthy and clear voice.Then a main factor is the voice of the singer,that needs talent and practice and techniques.Of course,the appearance of the singer or player is also important,healthy and sunny appearce is always the key.People have different thinkings about the main factors for success,these are my personal ideas.