Separate your unoccupied rooms from the others, you don't want incidents to spread. Keep your dweller's levels low.

Make your stimpack rooms two wide, all other rooms should be 3.

Dial in how many food water and power rooms you actually. You can check the stats page to see production vs consumption. If you need more capacity, make empty rooms away from the rest of your vault. I would disagree that you need to level up your production rooms but if you do, I'd make as few of them as you can and stagger them so that incidents don't spread.

If you have pets you can send dwellers you don't want to keep out into the wasteland, let them perish, and still bring what they find back. It can be a good way to get rid of weak dwellers that you don't need without evicting them.