Ding ding ding. The number one thing we could do for the planet is move everyone into "traditional cities". They don't have to be megalopolises, you can still have villages and towns of all sizes.

There just needs to be a very clear distinction between "people live, shop, go to school, go to places here" and "people don't live here, this is farmland/forest/nature or designated for nasty things we need", and the "people live here" areas need to be very dense.

That might mean a town of 10,000 that fits into 1 square mile (so you can walk everywhere in town and even into the countryside!), or dense cities with trains.