One interesting question always to ask is what happens they your characters die, or when an important object is destroyed.
This CAN change everything, The best example of this is Ned Stark, his dying made everything much more interesting then if he had lived. Never forget that a book can be sad, or depressing and still be good. It can not be boring and be good.
I am not saying you should kill characters just as a cheap way to make your book interesting. However it often will not occur to you because you have so much invested in them. You should think about how you characters would/should die, even just as an exercise.
For example, Spock in Wrath of Khan dies in a way only he would. It made the movie much better then if they had found some easy way out, it gave the movie a weight that it would otherwise not have had.
The Lensmen series is arguably the first real space opera series. If you are a science fiction fan you owe it to yourself to read it, for historical reasons if nothing else. Not that you should only read it for that, the series is a classic for a reason. While I could not fully describe it here I will list out what is more unique about it, and what sticks in my mind.
One thing that was a driving force of the series was the development of technology, specifically weapons and other systems on ships. One thing Smith understood very well is that the biggest secret of any new technology is that it is possible. Once your enemy knows that something is possible, they WILL find out how to duplicate it, it’s just a matter of time and effort.
The technology and tactics also evolved, new weapons forced new tactics, and new tactics forced new weapons. Very few books show this, even though it would be pivotal in any large scale conflict.
Second the scale of the series was very well done. By scale I mean that civilization (good guys) covered most of the galaxy, but it was not as simple as us having 2/3 of the galaxy settled and that part being safe and known. It was more like we have small number of stars settled and most of the rest mapped. But this is spread through the whole galaxy, so there are planets in the middle of civilization that are unknown, maybe even whole empires that have yet to run into us.
One, often subtle, distinction you need to make when your making cultures is the difference between cultural norms and limits.
A norm could be something like “Women should become mothers and stay at home.” But there could (and would) be exceptions, even if they were rare. If you made it clear that ALL women were wives and mothers I would assume that I was missing something. Also noteworthy is that with norms you might have no enforcement of this other then social pressure, mostly likely from the group itself.
A limit could be “Women ARE wives and mothers.” This would mean that there are no exceptions allowed. This would also mean that you would need something external to enforce it. There will always be outliers who want to swim upstream, even if they only want to do so to prove they could.
One area that I think is underdeveloped in Science Fiction is the effect of practical sexbots.
By practical I mean that they can, for most people most of the time, replace women/men for sex and companionship. I don’t just mean the obvious, but also being able to hold simple conversations.
Granted there will be some people who would never settle for a bot, but how good would they have to be until they change things in ways both profound and subtle?
How many resources and time are spent by men and women to attract the other? What if you could get your dream girl/guy for one month of pay? Would you push yourself as hard at work or in life in general?
The interesting thing about this is that making them is a engineering problem only. It’s going to be a while before you see them in Walmart, but we don’t need any big breakthroughs. We just a lot of time and effort. I mean it’s not like there would be a problem convincing people that it would be a good return on investment.