Every time an airline does one of these for
PR purposes, they've coordinated with ATC to get an expedited taxi, and continuous descent approach, and other special routings to save fuel. Regular flights don't get this kind of special attention.
Couple things an airline can do include cleaning up maintenance and painting processes, not carrying extra weight (catering supplies) etc., but it's mostly "greenwashing". You can do a bit with little stuff like turning off the hangar lights and using GPU power whenever possible, but it is a dirty industry.
Each new generation of airplane does things a little better, like LED instead of fluorescent lighting for cabin interiors, but you're not going to retrofit existing models for something like that.