What are the best cooking hacks you've learned over the years?

Brine chicken breast. I save brines from things like pickles and feta for this and choose whichever one best matches what I'm making. Feta + chipotle makes awesome burritos.

I always see recipes say to heat a pan until the oil shimmers but I've never been able to see the difference. Instead, I drop a couple pieces of diced onion into the pan and wait to hear a sizzle. This is extra helpful for someone with adhd like me who would absolutely start a fire if I didn't have a noise to remind me that I'm cooking.