There are several standard questions I am asked when I tell people I am writing a science fiction novel. One of them is how I can figure out the future, know what forms technology will take.
The real answer of course is I can’t. I would be a prophet, not a writer if I could. However that does not mean I don’t try. I will make mistakes and it won’t be perfect but that does not mean not to try.
When plotting out the future there are two major areas you need to be concerned with, the Culture and the technology. Most everything else is a function of one or of both.
The first thing to understand is that technology advances in leaps and bounds.
When a basic advance (such as the transistor or the first steam engine) is made suddenly a great many things are made possible. You see a flood of applications, and you see each made cheaper and more efficient.
When you are plotting out technology, the first thing is to figure out what these basic advances will be, then to spend time thinking about what they would change.
As an example if your future has a small, cheap and very dense source of power it would change a great many things. You would have to plot out all of these changes, and how they interact with the effects of other basic advances.
For example maybe the civilization developed the ability to make force fields fairly early, to protect a city, or a building. Once they have cheap power, they can make devices the size of a cell phone able to protect a person from being shot or stabbed or injured in almost any way.
The best advice I can give for understanding societies is to read history. Stealing from history is often the best way to make a people believable.
As in the case of Russia just after the communists took over. There was a huge backlash against fine art. Any art that was not seen as useful (like clothing or architecture) was looked down on. I integrated that into one of my worlds, although in New Europe’s case it is because they went through a bloody war followed by a couple generations of severe austerity.
The second bit of advice is that cultures rarely change fast, most major changes take a new generation to adopt. When they do change fast it requires something monumental to make the change. A war or something of similar scale.
The last piece of advise I have is to never forget that everything comes from something. Never have a movement come from left field. Have it sprout from a seed that existed beforehand. Think of it like a chain, each link leads to the next. If you are on the fifth link and we started on the first then you need to know what links two through four are. You may never have to bring them up in your book but you need to know them to make sure you have a coherent history.
Your culture will drastically effect how your technology develops.
The freer a society, the larger your middle class the faster their technology will develop. If you want your society to develop technology fast there need to be rewards on the corporate level and on the personal level for doing so. You also need education, you want as many people as possible to be able to contribute.