I usually play some scales slowly that require as little stretching as possible – just to get both hands working in sync and to get a feel for where I’m at. (Anybody who has played guitar more than a year knows that your comfort level changes from day to day. Some days you feel it – some days you don’t. Those days that you don’t require a bit more warm up time).
Then I move to through a few scale permutations that require more stretching, gradually building speed until I’m comfortable blazing through some difficult stuff. I try to mix up the right hand as well; alt picking, eco picking, sweep, hybrid, etc.
If I’m in a hurry, I like the 24 variations. (See lesson 75). This definitely works the left hand, but when you build speed it really helps the right hand as well. This one will get you warmed up fast.