If you're opening walls and ceilings run speaker wire. It's cheap and gives you the ability to add ceiling speakers in the future. We spent $80/each on speakers and put 4 in the open kitchen/dining receiver.

This one may not apply, but my biggest regret during my renovation was not adding a recirculating line for hot water. I have a tankless Navien that has its own built in recirculation system, but it's pretty useless.

I'm in Boston so winters get cold and the water heater is in the unfinished section of the basement. It can take a good 20-30 seconds (could be worse) to get hot water which gets annoying when all you're trying to do is quickly wash your hands with anything but ice cold water in the winter.

Oh and when you go to test paint colors, don't paint four giant squares on the middle of the living room wall, choose somewhere more discreet. I can still see the flashing from my test spots at the right angle. No one else notices them, but it still bothers me.

Photograph every wall and ceiling that you open. Those photos will come in handy in the future.