The fact is that you will not get better without practice yet sustained practice could cause repetitive stress on your bones, muscles, and tendons. Therefore, to minimize the wear and tear and ensure that you get the most from your practice time, it's prudent to complete a few warm up exercises.
I start by doing at least four repetitions of each task. The stretch should be held for at least 20 seconds and this task shouldn't be painful. If you feel pain while stretching then you are pressing too hard. There should be a sensation of extension of your muscles but not hyper extension. Hold the stretch for longer than 20 seconds only if you feel comfortable; otherwise, complete enough short duration repetitions equal the four/20 second sequence (420 ha! - I didn't mean that!).
It is important to note that you should have a planned practice routine. Everything you need should be organized and ready at hand prior to stretching. Setting up a practice routine coupled with organization can help expedite your learning curve and make learning easier and more beneficial.
I usually follow this sequence:
Neck exercises - Lean your head to one side and hold, then repeat in the other direction.
Shoulder rolls - I roll my shoulders forward then backwards.
Back stretch - clasp hands together and raise them above your head.
Leg stretching - Legs straight, attempt to touch your toes and hold - don't bounce.
Thigh - Bend your leg behind and hold your heel - you will feel your thighs burn!
I have photographed a few wrist and hand exercises.
Gently push your wrist against a stationary object and hold.
Reverse bend of the action listed above.
This therapeutic aids in building finger strength and flexibility.
Another view of the amount of resistance created by the web device.
After completing my stretching exercises I then set up my metronome to an Adagio meter (or slower) and run a three note per string scale chromatically from Low C to high C using the Major, Dominant, and Minor scales. Therefore, I'll start on the root of C and play a Major scale and wait usually four beats then play a Dominant C scale, then a Minor scale in similar fashion. I think it is important to play at a slow even tempo. This takes more time and helps simultaneously stretch and build muscles. Upon completion I stretch my wrist a little more because it simply feels good. I then double check my practice material and get to another round of productive practice.