Practice in the daylight from your steps.
Basically when the top of my stick is 1-2' below where I want the RoS (squirrel steps) I stand on the bottom step, unwind the strap (it's a sewn OCB), position it around the tree at the right height, pull out most of the slack, position the steps & tighten.
As others have said, tightening takes some practice. I don't mind some movement in my steps so I slightly relax the strap before tightening. Definitely more comfortable if there's no movement. To do that, I have to start tight & back off 1/8" at a time until I can get it to close. I've also heard retightening once on shaggy bark trees can help.
I wish I was a headlight on a north-bound train