Warming up should be part of your daily practice routine. The following exercise will help develop your picking and the discipline of keeping one finger per fret. Playing this to a metronome at a medium tempo will help your fingers warm up and make for a productive practice session.
For this exercise you should just use alternate picking (up and down and so on). I tend to to this exercise from the 1st fret up to the 12th fret at about 100 bpm. Once you get a little bored of it you can play with the order of the notes. Try 1 3 2 4, 1 4 2 3 and so on….
It can be tempting when you pick up the guitar to jump back into something difficult that you’ve been working on. If it’s a fast piece you run the risk of injury. Using exercises like the above can help prevent injury and will mean that after 5-10 minutes you’ll be ready to get stuck into something.