A common idea I see quite a bit is that all the good ideas in science fiction have already been done. The idea that you can’t write a book or tell a story because it won’t be about a new idea.
For such people I am going to put forth a few ideas that after reading science fiction, written from the forties to now I have rarely, if ever seen done.
First is the Afterlife, I am not taking about your brain being uploaded I am talking about the idea that your soul is real and it goes somewhere real after you die. I can only think of a few stories that have really dealt with it at all.
The Riverworld Series, and Traitor To The Living, both by Farmer, and The Night’s Dawn Trilogy series by Peter Hamilton are the only ones I know of that really deal with it. Kiln People by Brin dealt with the idea of souls but did not really touch much on the idea of an afterlife.
I am sure there are a few more but its not really an idea that you see explored much. Considering how profound any revelation of the afterlife could be there is a lot of room for interesting stories.
The Second would be having humans native to a place that is very much not like earth.
For example what if you had a planet the size of a large gas giant but had conditions like earth? It would have roughly two orders of magnitude more surface area then the earth.
If you were going to write such a story you would have to first figure out how the planet came to be and what would be different about its people because of it. In addition to that you introduce a problem for the main character to solve, and suddenly you have the makings of a good story.
You could also go really big and have people live on a Dyson Sphere around a star. While this has been done before it has not been done often.
Something I have toyed with is the idea of having a Dyson Sphere around several stars. One that is close enough to have real gravity for people living on it. At that close a range however any puncture would be.. very bad.
When you look at the history of armor and weapons during the middle ages one pattern you see is that weapons start to become more powerful relative to the armor of the era. Then you see the reverse where armor can stop any weapon. This repeats itself several times
Today weapons have won for the most part (fire enough bullets and they will in fact go through “bullet proof” glass eventually).
What if that changed? What if we had personal shields that could stop any projectile cold before it hits you? What effect would that have on society?
For example, what if the shield absorbed the impact of anything that hit it and distributed it across your entire body and, that it worked against any kinetic weapon.
This would completely change the kind of weapons people would use. You might have police lug around lasers that could only fire a few shots off per battery, or lasers that would almost certainly be fatal. You could have people make weapons that are made to transfer inertia and knock you on your ass so you can be tied up.
And of course nothing says that these shields have to be available to everyone. What if your ruling class was literately untouchable?
There is plenty of space for new Science Fiction the ideas here are just the tip of the iceberg.