Start with the basics
Most useful improvements are unglamorous: keeping water away from the foundation, testing well water and radon, making sure exhaust fans vent outside, servicing fuel-burning equipment, and handling old paint carefully during renovation.
Materials come next. When you're choosing finishes, look for disclosed ingredients and credible emissions testing, and make sure the product suits the room. The Materials Guide sets out the criteria Jacob uses.
Light, views, gardens and good layout make a house a pleasure to live in. They matter too, and they build on the basics rather than replacing them.