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Summary points of a good tablet pen grip:
1. Keep the pen VERTICAL (perpendicular) to the drawing tablet surface.
2. Keep your fingers as LOOSE as possible while still maintaining control of the pen. This requires a LOT less tension than you’d expect.
3. Draw with your ARM. Move your fingers and wrist only to adjust to your arm’s motion. Fight the urge to draw like you write (with your fingers and wrists in short motions).
4. Use the WEIGHT of your hand to apply pressure, NOT the muscle power of your fingers or wrist. Trust me, no matter how much you arm wrestle, your fingers and wrist aren’t strong enough to sustain hours of drawing without getting carpal tunnel.
5. Practice. Practice holding the pen vertically, loosely, drawing with your arm, and using the weight of your hand for pressure as needed. Practicing your grip and pressure is JUST AS IMPORTANT as practicing lines, curves, ellipses, cross-hatching, value drawing… You get the idea.