Have an explanation for the pace of advances
A mechanism that can speed up, slow down, stagnate, and even reverse itself...or just some rules of thumbs --- cylinders of a progress engine, if you will. When all cylinders are running, the progress engine runs well during and you see rapid technological advancement, yet the mechanism suffers when one or parts is worn or broken down.
Also, the same mechanism (or rules of thumb) needs to explain not only differences in progress across time, but across countries, as well.
There are many candidates -- war (or peace), plentiful food (or famine), relatively pleasant weather (or harsh conditions), long life expectancy (or short), religion (or its lack), you name it. Choose one. Choose twenty. It's all good, and it's your universe.
But you definitely need some sort of framework that works both for your story, and for your speculations.
Now, me? I worked up a crude map of technological paradigm shifts for the past two thousand years, when they occured, when they peaked, and when they stagnated, then mapped these changes against the estimated total population of the planet. I derived growth equations for each 'layer' of the ever-taller technological 'cake', making the whole sensitive to sudden improvements --- or collapses -- in the population, for whatever reason.
Why? I just couldn't quite accept that 19-20th century rates of technological progress were typical, on account they aren't, and it bears mentioning that there was quite an amount of innovation before the invention of the steam engine, too, perhaps miniscule from the perspective of this side of the 'Steam Singularity', if you will, but I suspect that the development of deep oceangoing navigation was a huge deal for the merchant marine of Europe in the late 1400s. It certainly worked out to be a big deal for the then-extant inhabitants of the Americans.
For pushing science forward, I needed some assumptions of what human population was going to do going forward. If we're mostly stuck on Earth, and the Terran environment degrades, then we're in for (a) first a significant slowdown in population growth, (b) a dramatic slowdown in innovation, and (c) at just the moment we could really use some practical applications based on all the neat-o ideas running about, resulting in (d) nothing much in the way of stopping the degradation of the resource base and environment of the planet, ergo (e) population crash and (f) technological collapse cascading us down, down, down the long, slow path back to foraging in the wake of packs of jackals.
Or not.
I wound up creating a host of scenarios, most more optimistic than the "Son of Malthus" tale above, yet even in the most optimistic, it will be quite some time before most human population growth is sustained by off-world (meaning off-Earth) population increase. In other words, at least for a bit, there will be (in my opinion) a tapping of the brakes (perhaps a slamming of same) on the progress engine that in my opinion has already been underway for the past 30 years (thus, no heavy-ion propulsion, no Mars colonies, only modest basic research relative to prior generations, and little more than cosmetic progress in consumer technologies).
Yet, that's just me, using a kludged-together spreadsheet chock full 'o' heavily-tainted assumptions to build a fictional future in a direction in which I want it to go...for purposes of story.
Personally, I want my warp drive, I want it hot, and I want it now.