Suburban Nation
Suburban Nation: The Rise of Sprawl and the Decline of the American Dream is one of the now-canonical texts of the modern urbanist movement. Noting it was first published in 2000 and has been highly influential, most of its ideas no longer seem novel - if you've been drawn into any of the online urbanist sphere (whether it be Strong Towns, Market Urbanism, YouTubers like NotJustBike or Reddit communities like r/FuckCars) then you've probably absorbed most of what it has to say.
For a very quick recap: suburbia as it exists today is the result of deliberate policy decisions and massive subsidies. It is economically non-sustainable and socially detrimental. The rise of automobile-oriented infrastructure has carved abysses through urban centres and hollowed them out.

The answer is to embrace the sort of urban design that led to flourishing urban centres for millennia. Mixed-use, dense, walkable neighbourhoods. All good stuff.

Instead of rehashing the general narrative of the book which has already become so engrained in modern discourse I just want to comment on a few points I find particularly interesting.
Design, Behaviour and Postmodernism
One of the trends Suburban Nation pushes against is the idea within architecture that design does not have behavioural implications. Nathan Glazer is quoted as saying "we must root out of thinking the assumption that the physical form of our communities has social consequence."
Having been introduced to urbanism in a post-Suburban Nation world and specifically through a lecture talking about crime and street design, that this stance ever existed has me surprised.
I do expect they are somewhat exaggerating the position and the extent to which it took root, but I think it does align somewhat with the trends of post-modernist architecture. I would be somewhat interested to read Nathan Glazer's From a Cause to a Style: Modernist Architecture's Encounter with the American City which outlines he's thoughts on modernism's failings. (It is perhaps worth noting that Suburban Nation also believes modernism failed).
So the failings of modernist architecture seem clear. Where they aimed to replace the ostentatious and elaborate ornamentation of more classical styles with functional, "rational" and "utilitarian" designs they failed to achieve either beauty or function.

The Infamous Pruitt-Igoe Apartment Complex being demolished
Postmodernism brought back ornamentation, but with a twist.
A Quick Tangent on Postmodernism
I'm not that knowledgeable about architectural style, but please bear with me. One classic example of postmodern architecture is 550 Madison Avenue.

As a building I think it is eh. It's not the worst thing I've seen but also not the nicest. At the time of its design though, it caused quite a hubbub of controversy. It was eschewing modernists' disdain for ornamentation in a very forthright manner. See the circle thing at the top? That was a reference to the pediments that adorn windows, and leave space for ornamentation. See below:

So the building is shaped like a window, it has a pediment, and then it references ornamentation directly through its noticeable absence. The whole thing is a bit of an architectural tongue-poke or inside joke (or "shitpost" as I've seen it described).
This is kinda neat... I guess... My problem with a lot of postmodernist art (including architecture) is that by being self-referential and containing essentially 'inside jokes' is that for you to 'get it' you need to be in on the joke. So the art necessarily becomes geared towards being in conversation with other artists, rather than the public. This has its place, for sure, but especially for public art I think there is a great deal of elitism to not design something for a general public rather than your own elite cohort of specialists.
You don't need to be "in on the joke" to understand, say, Art Deco, you can just think it looks kinda neat and then if you are more knowledgeable you can still get much more out of it. To me that is much more of a success for architecture than much of postmodernism.

Tangent on postmodernism over!
The conclusion here is that it seems perfectly reasonable to build something that is both functional, aesthetic (beauty has its own utility!) and for the general public. That is arguably what we had been doing in urban centres for millennia!

The Twenty Minute Home
A concept briefly discussed in Suburban Nation is that of the "twenty minutes home." The idea here is that because a home inspection is typically limited to a mere twenty minutes, then a sellable house needs to be able to market itself immediately and quickly. The result is large entrance atriums, inviting an immediate "wow" reaction, and then wide, open connections to most other key rooms allowing the potential buyer to quickly bask in the house.

This makes my inner materialist grin a little: a somewhat niche market circumstance having flow-on effects to design, which then structures how our day-to-day lives are lived. I think it is likely also somewhat overstated: whether you had twenty minutes or twenty days to inspect a house, I imagine grand entrances would still be quite popular. People like light, openness, and you can't rule out buyers wanting to impress their friends and visitors in just twenty minutes.
However, even if minute and subtle I still think there is something to looking how the current market facilitates real estate transactions and how that impacts architecture, urban design and the housing market.
Connecting the Public and the Private
Suburban Nation is highly supportive of mixed use zoning and organic approaches to growth. However, it is by no means a libertarian text and is quite critical of market-centric approaches.
For streets to be cohesive, it argues, buildings cannot be designed in isolation but collectively. In fact, the urge or architects to "stand out" when given the leeway is precisely what needs to be reigned in.
I'm somewhat more libertarian inclined than Suburban Nation in this regard. The failures of modernist architecture and urban planning can be linked back to large scale and top down planning, and while Suburban Nation has some suggested remedies for these follies I remain tentatively unconvinced. Aesthetic codes can quickly become red tape and hijacked by NIMBYs to prevent needed development; the codes can simply get it wrong, and I generally err on letting people do what they want on their property.
However I also do not think a full libertarian approach is feasible, and (the Georgist in me coming out) a libertarian view of land ownership needs to be quite complex.
However, I believe there is potential for a principled balance to be achieved by looking at the interface between the public and the private. Even if you hold private property as sacrosanct - that anyone can do whatever they want on their property - that does not extend to public property. How these realms connect seems of vital importance to me.
To give an example, drawn from the book, consider parking. Parking on private property still requires a connection to the public street, and it is well within the rights of the public to dictate how these connections should occur. Driveways that cross public footpaths, public nature strips, and require grading onto public roads (which then are built and signposted to accommodate them) is not the sole domain of a private property owner!

Drive ways along here would obviously greatly impact the public realm
So, for example, if public officials wanted parallel parking on a street and uninterrupted sidewalks, they would be well within their rights to do so and prevent driveways onto that street. Instead, they could offer an alleyway at the rear of the properties for automobile access (as Suburban Nation recommends).
Beyond driveways, the same principles could be extended to other entrances and exits passing between the public and the private. I think based on this you would be able to provide something necessary and enforce a degree of conformity that would support the cohesiveness of a street.
It is this interface between the private and the public that draws me to the metaphor of 'stitching the urban fabric.' It is about tying places together in a cohesive manner and joining them. I will likely expand on this idea in the future.
Final Remarks
Those are not necessarily the key takeaways from Suburban Nation but just a few of the more niche elements that I found interesting and not as broadly discussed as other key elements now well covered. I would still recommend the book if you are interested!