Practice is an essential component for progressing on a musical instrument. Serious musicians must often center their daily life around their practice schedule. Although there are many important musical fundamentals that every musician must practice, each person is an individual with their own goals and priorities.
In his masterful book, Principles of Violin Playing & Teaching, the revered violin teacher Ivan Galamian discussed practice technique in an extremely logical and comprehensive manner. One of his key concepts was in regards to dividing one’s practice time into three components: building time, interpretive time, and performance time. Building time practice encompasses all aspects of building one’s foundation and technique. This incorporates scales, arpeggios, articulation, full range exercises, etc. Interpretive time practice concentrates on all aspects of musicianship: expression, phrasing, style, and forming personal interpretations of the music one is preparing. This can be music for lessons, performances, auditions, chamber music, and larger ensembles. Lastly, he advocates performance time practice where one actually practices performing. This requires the musician to play current repertoire in larger sections or in its entirety without interruption or stops for mistakes and corrections. He also stresses the importance of mental alertness and using a critical ear when practicing.
As each player has their own musical schedule, the percentages for each of the three practice components will vary according to their own needs. For example, a student who is performing a recital in six months will do quite a lot of building and interpretive practice. As the recital date approaches, the focus would shift more to performance practice in preparation for the actual recital.
In any case, it is imperative for every musician to practice scales each and every day. Major, minor, chromatic, wholetone, pentatonic, dominant sevenths, diminished sevenths, intervals, etc. - full range in various rhythms and articulations. I am a big advocate for practicing longtones, as this allows singular focused practice on tone quality and fundamental checkup/review. Etudes are also excellent for practicing concentrated versions of technical and lyrical music specifically written for your instrument.
Articulation practice is also a critical component of a successful practice routine. Work to achieve quality and consistency at all tempos and dynamic levels, always utilizing different articulation and rhythmic patterns.
There are excellent study materials available for every instrument - ask your teachers and colleagues for their suggestions. Remember, the hardest thing about practicing is opening the case! So once your case is open, find what works most efficiently for you. The ultimate goal is to develop your foundational technique to the highest possible level in order to facilitate musical freedom on your instrument. Also remember, it is not how many hours you practice every day, but the combined results you will achieve from consistent, focused, and efficient practice.