Definition of predating
If the steampunk results from Applied Phlebotinum, see Phlebotinum-Induced Steampunk.
Many examples of steampunk mix in a few mutated monsters (probably in homage to Charles Darwin living roughly in the era depicted), thereby bordering upon biopunk.
Jules Verne, the first Speculative Fiction writer, is the king of this trope. For added style, however, knowledge of the New Thought movement can help, as can Spiritualism, as both of those were very popular among the Victorians, and very influential on their thinking.
In addition to being a science fiction writer, Jules Verne was also a Naturalist.
The steampunk Naturalist, as exemplified by Verne and others such as William Beebe, is one of steampunk's most important subtropes.
If instead of industrial era technology, the setting has pre-industrial technology, see clockpunk, and if it includes internal combustion engines in place of steam, see dieselpunk, though there can be crossover between them if used purely aesthetically.
Legacy HALs (also deprecated in Android 8.0) are interfaces that predate conventional HALs.
Supernatural or paranormal tropes are more frequently included in this approach, in which case the favours "Gaslight Romance".
The more Victorian branch of steampunk sometimes also incorporates vaguely Lovecraftian elements, as shown here.
Another good example of the Lovecraftian/antediluvian influence on steampunk would be the design of the Expect to also see a strong, visible Irish influence, in terms of such features as stained wood, brass, and American frontier-style blown glass oil lamps.
You will occasionally encounter some minor overlap with the post-Victorian Art Deco movement as well, particularly in terms of typography.
The Zeppelin or rigid airship could also be considered one of the major icons of steampunk, due to the major public enthusiasm for the craft pre-1937.