My old boss told me to always run a second wire pair for future use
Back in 2012, he said 'Just pull an extra 22/4 while you're in the wall, you'll thank me later.' I thought it was a waste of time and cable. Fast forward to last week, I had to add a glass break sensor to a 10 year old install. The extra wire was right there, saved me a whole afternoon of fishing. I've used that trick on probably 30 jobs since then. What's the best piece of old-school advice you guys still follow?