Inspection and Codes
Know your codes (or hire someone who does). If you're rebuilding a wall or changing the floor plan, you might as well have the proper amount/spacing of outlets and think of any possible scenario in the future that may require a plug nearby.
Imagine a live band playing on the front porch at your New Year's bash? Fancy one of those must-have self-heating toilet seats? It's cheaper to run wire for speakers through an open soffit now than it is to decide you want some tunes in the family room after you have installed the drywall, taped and painted. If you think you may want it in the future, try to make decisions in the correct sequence.
Do A Dry Run
Before your kitchen faucet reveals its ugly leak during your housewarming, test everything. Turn on the sprinklers to examine proper drainage, take a shower, do a load of laundry, and run the dishwasher simultaneously to see if there's enough water pressure to enjoy that shower and ensure there aren't any leaks that could ruin the new suede faux finish in the study below the master bath. (Yes, it happened to me ...)