- End the war on open source and instead embrace it. This unlocked a lot of potential and put a stop to a lot of counter productive efforts in MS where the only point was "not invented here". Some of these things were already tolerated grudgingly under Balmer but Nadella made it company policy to embrace it 100%. There are many examples of this ranging from reviving .net via the mono ecosystem, launching mssql on linux, making linux a first class citizen on Azure (now a key driver in the valuation), vs code studio, the github acquisition, embracing chromium, etc. Through this, MS regained a lot of the street credibility with developers that it used to have in the nineties and subsequently lost.
- Kill off windows phone and de-emphasize the windows brand in favor of an office on any platform type approach. Office now runs great on ipads, os-x, browsers, android, as well as windows laptops. Not having the distraction of windows first means all the non windows teams that are making lots of money (azure, office, etc) can now focus on doing the right thing on non MS platforms instead of up-selling windows to their users. Balmer left Nadella one huge headache which was the Nokia acquisition (I used to work there). Nadella killed that off swiftly and decisively by effectively starving it of resources and almost immediately cutting staff by the tens of thousands.
- Fix the toxic work culture. There was a lot of negativity around this topic under Balmer. It seems much less of an issue these days.