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I would imagine that depends on what you need to work on. As a beginner, I don't have a book of exercises, just Suzuki volume 1. My teacher recommends lots of scales (so far just 1-octave scales in A, D, and G), as well as using the easiest and most familiar tunes (Twinkle, Lightly Row) to play when working on things like placing the left hand fingers properly and developing a fluid motion of the right wrist. The idea is to use a piece that is so familiar you can think about the technique and not about what finger to put down next.