Pillars of Steampunk

Steampunk is a hard genre to pin down. As one of the newer subtypes of science fiction, it still has a relatively shallow literary library (both in terms of the number of books and their general quality) compared to its parent, cyberpunk. There's also no widespread agreement on what makes something steampunk versus not.

To help do a rudimentary breakdown of steampunk, let's look at the three S's: science, society, and style.

Science

This is required by the "steam" element - if you don't have the right kind of science, you're general sci-fi, not steampunk. Without the science, you become a historical piece.

What kind of science is right for steampunk? First of all, steam power. Steam needs to be the primary motive force involved, rather than fossil fuels or other fuels. Gas and oil can be present, but should be rare. A possible exception is a story set in the transition between steam and oil, where steam is in the decline. A futuristic take is steam power generated by advanced technology. For example, nuclear reactors are actually steam turbines. Many thermo-energy plants and solar energy plants also use steam.

Next, you have a whole host of mid-to-late 1800's science concepts. The aether is one of the most commonly used. Also common was the rise of logicians in math. They believed that through pure logic everything could be proved and, in turn, science could know and determine everything in the universe. The science should be derived from those early ideas, before there was quantum physics. Leave out Godel and Heisenberg and focus on a physics with hard deterministic consequences.

Society

This is required for the "punk" half of the name. There was a lot of tension in society at the time: colonialism, the rise of capitalism, the scourge of Luddites and cronyism, Social Darwinism. Money was being released from the hands of an elite few and spread to the masses. The old aristocracy fought back with claims of genetic superiority and the use of social forces to control and reign in the newcomers.

This is when a person with great ideas and abilities could earn their fortunes - but at the same time have to fend off the predators who sought to seize their momentum. The emergence of the middle class was tumultuous and is just one of the many aspects that can be present in good steampunk.

Style

Style is just a generally nice thing to have for reader interest. For example, vocabulary. Victorian era words are incredibly important for setting the tone. This doesn't have to be everywhere - a little goes a long way. Likewise, writing with a higher end vocabulary (college level minimum) reflects the writing style of that era, which was aimed at an educated audience.

And of course you have action. A rousing tale of adventure and exploration fits well within the spirit of the age. Seeking the unknown is a great theme, whether it be in the external or internal world. (After all, Freud and psychology are very Victorian.)

There are likely more elements. When it comes to style, I would say Romanticism works over Naturalism (a topic for another time). And when it comes to specific themes, they are numerous and I've only briefly mentioned a few above

Sadly, most steampunk stories have plenty of style, but very little of the science or society aspects. As a result, theycome off as vapid and shallow, having very little stand-alone value apart from being a bit cool because of their aesthetic. A truly deep steampunk novel will combine all three and be written in the romantic style to represent a clash of values of the era.