I don't meditate before I play or compose, but I see playing and composing as meditative acts.
Occasionally, when I run into a great bass backstage at a festival I'll play a few notes on the low E string, just to feel the instrument vibrate against my belly.
I found it liberating of necessity to devise my own style and my own tactics and to look for a voice on the instrument because there weren't really any that impacted strongly on me.