Thus far in my series of steampunkery, I've talked about weaponry, vehicles, aeronautics, clothing and various other considerations you have to take in account when crafting the story. But how, you might ask, can you draw all this together into a world that has the verisimilitude needed to be an authentic steampunk setting?
Well, there's two major ways you can go about this. The first, of course, is pick all the facets of steampunk you think are cool, throw in a big ol' blender and hit puree. The second, and probably more logical method, is to consider how you want your world to have developed.
Since the first method is comparatively easy, I'm not going to expound on it here. The second method (the one I attempt to do) is much more difficult, but results in your world having a much more authentic feel than the first. There's also nothing that's stopping you from writing the first draft using the first method and then performing the second method in subsequent revisions. Moving on ...
The old saying "necessity is the mother of invention" applies to a fictional setting the same way it applies to history. If you look through the historical record, you can probably find examples of inventions that came about because the inventor saw a need for it and realized there was nothing to fill the gap. Archimedes developed his water screw to improve the method of getting water uphill; Alexander Graham Bell invented the telephone to help people communicate; Galen developed the traction table as a better way to set broken bones.
For your steampunk setting, you want to consider (briefly) how your world developed and what innovations would show the greatest benefit to the populace. Airships allow people to avoid rough terrain that would've otherwise slowed them down; steamships allow quicker transoceanic crossings; steam-powered vehicles transport materials in greater quantities at speed than horse- or ox-drawn carts, etc.
Mechanized looms developed to speed the production of cloth thus speeds the production of clothing, which also might result in cheapening the quality of the clothing (not necessarily, but work with me here). Each invention has reasons for coming into being and consequences that result from it becoming popularized.
You don't have to do this for everything, mind you. Just the major innovations that have the most effect on your fictional society as a whole. War machines are easy -- humanity has always looked for more efficient ways of killing each other (and that's not hyperbole, though some days I wish it was).
As with much of the background research we authors do, this whole process will probably not show up at all in your text. Except for those steampunk machines that are needed for the plot. Which is yet another item you need to think about in crafting an effective steampunk world.
If you want any clarification on these rambles, feel free to ask in the comments or send me an email. I'm more than happy to explain myself further.
NOTE: The map of an alternate North America was taken from the website The Adventures of HMA Badger, who is part of a group called Steam Century that runs steampunk mystery games throughout the Upper Midwest of the United States.