Simon Fisher’s violin exercise books Basics and Practice are a treasure trove of focused excercises and a worthy addition to any violin student or teacher’s library.  One amazon.com reviewer says “the sort of book you would wish for if it didn’t already exist.”  I have included the amazon.com link but you would probably get it cheaper and easier from Edition Peters.  Basics Practice

The Art of Violin Playin by Carl Flesch is a monumental and comprehensive treatise on everything imaginable related to violin playing.  It covers body posture, left arm, right arm, tone production, practicing, musical memory and more.  Many consider this work to be the bible of how to play the violin.  It is an invaluable resource for the violin teacher and advanced student.
You can read a discussion of this book at violinist.com here.

After practicing for three or four weeks from the first day I touched my violin in twenty years it became abundantly clear that I needed some professional help.   It took me another couple weeks at least to get the nerve up to ask our orchestra teacher if she would be willing to give me a few lessons.  I was so nervous when asking, “do you think you could give me some lessons.”  Why would anybody want to teach an adult with little hope of achieving anything?  Wouldn’t it just be …

Galamian’s Principles of Violin Playing and Teaching is a classic of violin pedagogy.  Often considered oe of the most influential teachers of the twentieth century teaching great violinists such as Perlman and Zuckerman Galamian developed his principles and methods which are masterfully detailed in this book penned by Elizabeth Green at Galamian’s approval.