Love them or hate them there are a lot of common tropes across the science fiction genre. What are some of your favorite and least favorite tropes?
I think it goes without saying that one of the least favorite tropes is Deux ex Machina. I couldn't quite put my finger on it at first, but after watching the German TV show "Dark" I was utterly dissatisfied with it. The entire series up until the very last episode is about this inescapable time loop and alternative universes which is pretty cool while watching it, but then you get closer and closer to the end wondering how they are going to solve this impossible problem. Then surprise they just do it instantly in the last episode.
Another trope I am not very fond of is nanotechnology where there are trillions of tiny robots that can effectively act as magic. It just feels like a lazy way to write science fiction because you really want a fantasy.
A trope I do actually like despite how overdone it is, is the idea of a precursor or forerunner. It often brings to light the absolutely massive scale of the universe which I find fun to think about.
A trope that's bothered me more and more over the years is planetary chauvinism. So many science fiction settings make the assumption that people will only ever live on planets - and usually specifically Earthlike planets - and anything else is just something for a mining ship to visit, when it's even thought of at all.
A somewhat related issue is the grand importance that Earth always seems to be given. I can understand it from the perspective of writing stuff for the general audience, it's super easy to make them care about whatever's going on by saying "oh no, Earth might be destroyed" but once we're a couple of centuries or millennia into being a spacefaring civilization with colonies all over the place Earth is going to be just one planet out of many. Star Trek is a particularly bad offender here since not only should there be plenty of human colonies just as big and important as Earth at this point but there are dozens of nonhuman Federation members too. The Federation didn't end when Vulcan got destroyed, it shouldn't end if Earth gets destroyed.
For the second concern i like the two Hainish Circle books i have read, "The dispossessed" and "The left hand of darkness". They mention that something like earth exists, but it's not even a plot point, it's just another planet. But then again these books are social commentar / thought experiment first and foremost, they just happen to be in a Sci-Fi setting.
Necroposting to suggest the The Culture books by Ian M. Banks. The vast vast majority of people live on big space habitats like ring worlds, O'Neil cylinders, and Stanford Torii. Also some of the hugest ships carry basically a whole planet of people.