This is a given, but I for one can’t play worth squat if my fingers are cold, so room temperature is pretty important. I used to have a portable mini-heater that I’d sometimes use directly on my hands if I was cold. Made a big difference.
Warming up is also key of course. You really have to listen to your body…if your fingers are telling you they aren’t warmed up enough yet, don’t force things, continue warming up until you know you’re at a 100% functioning level.
Stretching exercises of course too (after you’re warmed up).
I’d imagine consistent repetition of warming up and stretching before practicing would eventually get your fingers more limber and less tense.
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