Etudes! I used to play these more than I played anything else.

Kayser Op. 20 – 36 Elementary and Progressive Studies For The Violin
Kreutzer – 42 Studies Or Caprices For The Violin
Mazas – 75 Melodius and Progressive Studies – Op. 36
Schradieck – The School of Violin Technics
Wohlfahrt Op. 45 – 60 Studies For The Violin