As any musician will tell you, warming up when you practice or perform is essential! No warming up (or warming up incorrectly) can lead to damage that may be irreversible. I didn't pay much attention when people told me to warm up and ended up having to take a couple of months off playing. I count myself quite lucky, as if I had carried on down that road, months off could have turned into an eternity.
One of the most common warm up exercises for guitar has to be the Spider Exercise (some people call it Chromatics). This normally uses all four fretting fingers and is played ascending (going up) or descending (going down).
When using as a warm up, start slow and build up. Carry on if you want to use it as a technical exercise to improve your technique.
Read my article here. Stay tuned for parts 2 & 3!
Until next time!