It used to be called 'Environmentalism', or 'Conservation'. We think of it more as 'Planet Saving', because if we end up Venusizing this place we don't have another one handy we can move to.
Solar Power: Obvious.
Wind Power: Equally obvious.
Micro-houses: Use less energy, lose less to waste heat.
Arcologies: Economies of scale.
Species Preservation: Try to save what we've still got while we've still got it. One major focus is the preservation of native bees. Honey bees in commercial use are commonly seen as the only bee that needs saving, but in reality, there are thousands of other species that do the real heavy lifting. Most of these bees are in steady decline and at least three species are already extinct.
Depaving: Asphalt sequesters less carbon than trees do.
Permaculture: Don't make the mess in the first place and you don't need to clean it up later.
Toxin Straining: Cleaning up some of the crap we've already let loose.
Anti-Lawn Culture: The use of lawns for a useless, often ugly, crop (grass) that uses excessive amounts of water while leaving no room for wildlife or native plants is gone in a solarpunk world. Lawns are fully utilized as gardens or "meadow gardens" instead of used as a status symbol.
Rewilding: Areas that are not being used or are not good for farming are allowed to return to their natural state.