Flesch is quite good, I would also suggest Hrimaly Scale Studies (which I use). Heifetz really loved this book of scale studies he used this scale system and taught it to his students. Also along with your normal scales, make sure to do third, sixth, octave, fingered octave, and tenth scales in every key.
Hrimaly Scale Studies for Violin
Series: String Method, Scale Studies, Violin Method
Publisher: G. Schirmer, Inc.
Composer: Johann (Jan) Hrimaly