reaching down and twisting 90 degreees is a good one....
BUT in my opinion, everyone has a different grip..... for example me as a retired linesman, back in the day,..... could twist just about anything in front of me....
here's what I do... right or wrong. I get my handy dandy coat hanger with a "O" ring on it, to make sure the axle is straight, and I eyeball tighten it...
then I take it down my long drive way... if it jumps sprocket, I tighten it up a couple of cranks and try again...
if it doesn't jump sprocket, I'll do the reach and twist... if I don't like it, I loosen it, til it jumps sprocket... and retighten a couple ....
Mine is so loose, that when the rear wheel is off the ground, my belt lays on the swing arm axis....
As of the life of that belt.... I've heard anything from 35k to 100k.... I'm pretty sure the higher number is normal.... BUT some of our belts have let go at much lower miles, with no known reasons. And then again, I know of 2 X's with tears/holes in their belts, and have put huge miles on them with no issues... I have no known reasons or theories on why any of that is what it is....