Here's my tips for loosening up
- Breathe. Take some slow, deep breaths until you feel youself loosening up.
- Open up your hands, extend your fingers and shake from the wrist. Just imagine that you are trying to shake water off your hands. Do this for 30 seconds or so, and you'll loosen up your wrists as well as your fingers. It also promotes bloodflow to the area.
- Stretch your wrists and forearms. Tendons in your forearm and wrist affect movement in your hands and fingers, so loosen them up. Put your palms together, point your fingers away from you and move your forearms toward your chest. Then repeat by pointing your fingers downward, upward, and towards you.
Running you hands under warm water is a decent idea, but I would make sure that my hands are COMPLETELY DRY before performing. Playing the bass with slightly wet hands is not only detrimental to your strings or fretboard, but it can damage your calluses by softening them up and making them easier to rip. Also, if then venue is cold to begin with, warm moist hands will turn to even colder hands than you started out with. I prefer to rub my hands together for heat.
