The first step is to eliminate cars as a primary mode of transportation.
>>>>The first step is to make it possible to live without a car.
>>>The first step is to set up separated bike lanes and improved electrified bus/rail routes.
>>The first step is to convince the legislature to shift infrastructure funding away from building new roads.
>The first step is to elect the right candidates, build a base of support, and draft an amendment which can get through the next budget showdown.
And so on...although it's more of a sprawling tree than a descending list.
That part's made even more difficult by there typically not being any right candidates at all.
You not only have to change planning, you also need to change all the existing cities to accomodate that planning
What
On the other hand, I, too, want to live in a house with a green space of my own, and would complain loudly if I was forced to change
There are a few exceptions like London (7 million in the 19th century, 9 million now), but most cities are not London.