The thumb rule for good riding is to think of the upper body as a mechanism of control over the motorcycle. The lower body has considerably more physical task of holding on to the motorcycle. So how hard do you think you should be holding the handlebar?
The correct answer is just firmly enough so your hands cannot be thrown off by an unexpected bump. But no harder. The more nuanced answer is that you should be able to maintain this light but firm grip at all speeds. Obviously, this is harder than it sounds.
More importantly, how you’re holding the motorcycle - pen, handshake, vise, claw or talon – is a good diagnostic. Any time you determine that you’ve lost that light-firm grip to something harder, you know you have made or are about to make a riding error.
One common error is a body position problem. You’re holding on in a death grip because your lower body isn’t holding the motorcycle firmly enough. You either just let go or the motorcycle is slippery. I would consider this a critical issue to tackle because it fixes so many corollary issues and improves feel and confidence disproportionately.
The other reason for the death grip usually is rising tension. Sometimes the apprehension you’re reacting to isn’t obvious – you realize it later when your hand starts to hurt. But odds are that the disquiet began with what your eyes saw and how your brain processed the visual input. The tension comes from a rise in perceived risk. It causes you to naturally tense up and the grip becomes hard.
A hard grip causes disruptions in your ability to modulate finely the throttle aw well as steering. It also causes other problems.
But the important thing is to find and quell the source of the tension. It could be something as simple as needing to slow down a bit, reorient the eyes to look further into the corner and reduce the sense of speed. The tension is a sign that your brain is reading a higher than normal risk, and you really should pay attention to that.
What you could do is the chicken check. Periodically flap your elbows about to remind yourself that your upper body should be relaxed when you’re riding. That’s all it takes, really.