Of course the most difficult thing on the violin is always intonation. The second one is rhythm. If you play in tune, in time with a good sound that's already high level. Those three are the main things.
Ruggiero RicciEvery violinist has a different style, so it's important to be able to recognise their styles. You don't have to like everyone's style but you have to know these styles.
Ruggiero RicciSo, first you have to be able to play with a metronome. Then you take your freedom. If you play in an orchestra, you got to watch the conductor, he is like a metronome, but it is more difficult because he can change rhythms.
Ruggiero RicciI don't have favourites, I think, when you play, you have to be like a prostitute, you have to love the piece you are playing. Even if you don't like it, you have to play it as if you would like it. Then you are a good interpreter.
Ruggiero Ricci