I squeeze gently - you can desensitize your fingertips if you squeeze (or thumb) too hard. I started flying in 1969 (age 12) with a Heathkit transmitter that was too thick for me to 'thumb' comfortably. I sort of flew in single stick mode (but mostly 3 channel airplanes), only adjusting the throttle when necessary. Until I started using a strap (which I cannot fly without, now) I would thumb the left stick and pinch the right (mode II). I hate holding the TX, it seems more comfortable to me to rest my hands (which are on the small side) on the TX face. Every once in a while I will hook the strap on so the hook part is not fully extended. Invariably at some time during the ensuing flight the hook will shift causing a momentary (and fractional) drop of the TX which always provides a nice little adrenalin rush [X(].
Happy Flying (however you choose to grasp the sticks)!!