The Practice Environment
When students practice, they should have the following:
1) A pencil to mark notes on fingering and bowing in their music as they practice
2) A metronome
3) An A440 pitch reference (can be built into metronome, tuning fork, keyboard, etc)
4) Mirror (preferably a wall or door mounted mirror) so they can study their bowing, posture and left hand technique
The practice space should be free from distractions. Student should have a water bottle and drink 16 oz. of water an hour. Every hour the student should take a 10-minute break to rest.
Many teachers encourage their students to have a stretching routine before they practice. Stretching muscles releases tension and can prevent injury. A google search for "stretches for string players" returns many results with stretching examples. This article in American String Teacher is another resource:
Russell, J. and Higgins, P. (2013). Avoiding Discomfort and Injury in Young String Players: A Stretching Activity Guide. American String Teacher (63) 2 (May 2013), 21-25.