Steampunk was coined in the 1980s and became more well-known during the 1990s as a somewhat flippant riff on the term cyberpunk. In many ways, it's just an aesthetic, not a genre per se. Even the earliest steampunk didn't necessarily have any genre conventions; it just had a lot of references to steam and clockwork powered technology; a kind of runaway Victorian era, if you will. As steampunk has matured and evolved into this decade, that's if anything, been an even stronger focus on the movement; it's more about a sense of style, a look, an aesthetic, than it is about anything else. There's not a "steampunk worldview" or conventions of a "steampunk story" that need to be met other than an application of the aesthetic. Heck, Disney did a line of steampunk pins that illustrated this concept more than anything else; putting a mechanical monocle on Pete was nothing if not pure aesthetic overlay.
Me, however, see, I like to use steampunk as a label that's closer to its roots in cyberpunk. It's not just steam-; I also need to have a hefty dose of -punk. So to me, urbanization, dystopian societies with all kinds of social ills--a kind of exaggerated Dickensian London approach--are as important as anything else to be steampunk, not just wearing tophats and goggles. I also shy away from a pure Victoriana approach, mostly because I like fantasy that takes place in the so-called "secondary world"--an author-created world, not the real world that's been "fantasied-up." There's no Victoriana, because there's no Queen Victoria because there's no Great Britain at all.
That said, I backed off from some of my earlier approaches, where the steampunk aesthetic was fairly prominant to one in which it's fairly low-key. Rather than run-away crazy steampunk inventions, I only have a handful of clockwork and steam-powered devices, and rather than letting my stories and games and settings really hinge on them, they just provide some background and color here and there.
One way in which I've done this is to suppose that urban areas--some of them, at least--are known for having clockwork "bugs" that crawl around on the walls and streets and rooftops, taking messages from one place to another before needing to be wound up again. They don't speak; you can just fold up a parchment message, put it in a small container in the bugs chassis, and then let it go. Because these bugs are large enough to resist tampering by birds, cats, or other wildlife, yet which crawl around in areas where other people cannot easily intercept them, it is seen as a fairly secure way to send message across town without having to go in person.