Have you ever seen the video by John Petrucci on how he warms up? He stretches everything from fingers all the way through back muscles. I always stretch my hands, fingers, forearms, shoulders and back. Just basically loosen up the whole upper body, but with emphasis on fingers through the elbows. I have a couple extra firm grip squeezer things and I usually do 20 reps each hand, then squeeze them shut and hold them for 10 seconds. I do that before I even walk in the guitar room. Then I stretch fingers and hands while I'm in there. Usually before I play anything but many times I'll play a little first. Sometime around 10 minutes into playing, I stop and stretch my hands, fingers and wrists one more time. THEN, I'm ready to cut loose.
Having been into sports all my life, I always knew the importance of warming up and stretching before games. Never did it for guitar though for many years. I always noticed that I wasn't as sharp when I first started though. And that if I walked in the room and started trying to rip immediately, I was not as sharp as I was after I'd been playing for a while. Heck, I remember many nights playing for as long as 30 minutes. Then ripping into something and realizing how much easier it was than when I first started playing that night. Then I saw the JP video and started actually warming up some and stretching a lot. BIG difference. The funny thing is, it really is like when playing ball or something. I can go run up and down the court a few times and am still a bit tentative. After a few minutes I'll really open up and run, cut, etc. full speed without worrying about pulling something or blowing something. I always run across the outfield a couple times forwards and backwards before playing softball. Same principles apply here.
Now, even if I'm playing blues or strumming chords, I stretch the hands thoroughly. Even on the stuff that requires less dexterity, it really helps.
IMHO/YMMV/CYPFELO4H