One thing I have seen a few times is a main character in a book being the first to do something that should have been done well before hand.
For example, if I was writing a book about the invention of a replicator I would expect that it would take about a week for someone to note the many ways it can be used as a weapon. Or use it to make drugs. Or for that matter to have it create an explosive that would be so unstable it normally could not be moved, therefor used.
If your character is the first person to do something, think about WHY this is the case. Would they really be the first ones?
The thing about world building is that you CAN do it for years, and never finish. After all if you wanted to write a backstory of a world with the same level of detail that we have for the Earth how long would it take?
I can’t say how others do it but I tend to do my worldbuilding in stages. When I was starting to write my first book I wrote enough about the major powers, and enough of the overall timeline to have a basic idea about what was going on. I needed to know what kinds of tech they would have and stuff like that.
As I finished the first draft I realized I needed more so I gave it another pass and added many more details.
Around the fifth draft I did one more last long pass, I went into detail about all the major political factions within each power, enough that I could write stories set anywhere I wanted.
I did this in stages partly because I did not know what I needed until I got there. It was also helpful because worldbuilding is some of the most brain taxing work you will do, doing it all at once can be hard to impossible.
If you are from the west a great many things will be normal are VERY abnormal historically. I am not saying you should just assume they change back, but don’t assume things that started changing fifty years ago, and are changing today will freeze as they are now.
For example, for most of human history, people were adults when they could do the work of an adult, for a woman this was somewhere between puberty and 16 or so. For a man, this was when he was big enough to farm/hunt. Adolescence did not exist as a concept.
If I was forty and got engaged to someone who was sixteen I would be, to say the least, looked down on today. No one would have cared a few hundred years ago.
I don’t think I need to say how much EVERYTHING surrounding sex has changed in the last century, there were times and places when women would not let themselves be seen when pregnant (not even in church).
Various societies have changed how they used makeup, from only tacky women using it, to men, to everyone.
For those of you (hopefully few) who have not seen A Taste of Armageddon, it is set on and around the planet Eminiar VII.
The Enterprise is sent to open relations. They know little to nothing about Eminiar (Its location would make it a very valuable ally).
It turns out Eminiar and its neighbor (a former colony) have been at war for 500 years. The war, however, is being fought with computers. The linked computers determine if someone was “killed” in a simulated attack if they were they have 24 hours to report to a booth for their death’s to be registered.
The idea was that neither peoples were willing to give up the war. Nor were they willing to devote their entire economy to it, nor destroy so many things of such great value. So they found a way to have their cake and eat it too.
This episode has two great things of value for writers. The first is that the people of Eminiar thought the war they fought was just how things were done, to the point they only explained it when it became obvious that Kirk did not know what was going on (he asked why they were talking about a nuke going off when they enterprise detected nothing). They fought tooth and nail to keep things the way they were, it was not a good way of doing things but they saw no other way.
99% of people see the way things are as normal, you must keep that in mind.
Secondly, it asked very big questions without bashing your head with them, nor did asking them slow things down. Questions about the nature of war, why it should be fought. Really heavy ones.
Allegories can be powerful, but they are like icing on a cake. You first need a good cake, then you need to make sure you don’t weight it down too much. Subtly is the name of the game.