Took a yoga class a year ago and picked up some stretches that are awesome for disc golf, as far as rotating the entire trunk of the body, working the back, shoulders and groin/hamstring all at the same time. So I do about 10 min of stretches before a round--I advise all to pick up a yoga book at the library and check it out, some of these simple positions really improve physical (and mental) health.
If I'm playing with friends I try to get them to play catch with me for awhile before a round, usually with a Classic Roc or Aviar. Helps my timing, gets me running around, gets the blood moving.
If alone I first throw maybe 50 putts, all within 25 feet, making sure I finish with five in a row from 15 feet since missing those makes me want to tear the basket out of the ground. Then on the first tee I throw all my putters as warm up drives.
I freaking hate it when I'm playing with someone who wants to just hop out of the car and start chucking discs, my score always suffers.