This came up last weekend taking my nephew to the range. For a new shooter, I have a cheap stopwatch with a start button at the top of the device. I show them that there is about 1/4" of takeup once the meat of the finger starts increasing pressure on the button and meets resistance. The button has about the same travel distance as a Glock trigger pull and will noticeably bind if the pull isn't straight back towards the device. My verbiage for trigger pull is to "slowly increase pressure while maintaining the 'equal height/equal light" on the sights."
I've been able to help cure some people's consistently shooting low-left by emphasizing the mechanics of the finger as it contracts and a focus on increasing pressure straight to the rear. FWIW.