Mary Kole, who was a literary agent for the Andrea Brown Literary Agency, created this list of questions to ask your characters.
K.M. Weiland, a fiction writer who has also written writing guides, addresses two key questions to consider: What lie does your character believe? What happens when they discover it was a lie?
John Fox has created his "Gigantic List of Character Descriptions" with plenty of concrete examples from literature: https://thejohnfox.com/2016/06/character-description/
Even if Sci-fi isn't your genre, you can still glean helpful information in this article by Charlie Jane Anders titled "10 Tips and Tricks for Creating Memorable Characters."
For more writing advice via Gizmodo, a design, technology, science, and sci-fi website, click here: https://gizmodo.com/tag/writing-advice