It's a challenge that I have always struggled with. A recent example of this situation caught my eye yesterday.
I used to write fanfiction, that's how I got started. I still read the stuff. I was reading a story set in the universe of a a sci-fi series with multiple non-human races. Doesn't matter which one. The point is that tv programs produced in the US are written by Americans. No matter what kind of makeup or costume they wrap the actors in, the 'aliens' on shows like that almost always think and act like modern Americans. However, this story was different.
This particular fanfic includes an alien character that was forced to make a difficult decision. She married a human, and used genetic engineering to artificially craft a child with him. Her government vehemently disapproved. Her government ordered her to abandon her husband and her baby, and return home to resume service to her people. She obediently left her child behind to be raised by the father, and never looked back. It broke her heart. But she did it because her ethical system considered obedience to authority, and the needs of her people at large, as being greater than anything else.
There are human cultures, or that have been, that might have reacted in similar ways. It's just that most Americans bristle by reflex at the concept of that type of submission to authority. This is not the kind of thing that most Americans would do, of either gender. The average American, if faced with that kind of ultimatum, would react in a way somewhere between telling their C.O. to kiss off, or perhaps make a run for it, or even possible murder. Most of us would not consider abandoning our family because the state demanded it. But that does not make it an invalid choice. She had reasons for her decision.
It is unusual in the extreme to find a story, or a show, where the aliens actually act un-American, much less alien. Not that this particular situation was really that weird. But it did veer away from the usual fare. Which is one of the main functions of sci-fi. To make the reader stretch their imagination and consider what-if.
My fiction has non-human races in it. I haven't dug too deeply into their mental or emotional makeup, because I am uncertain about how to present it. But speculative fiction is even more effective at provoking authors into considering what-ifs.