A question that has popped up a few times is, "Do you start with plot or character?"
Really, the FIRST seed of a book is usually a premise that includes a hint of plot, character, and setting, such as, "A mermaid who likes to read falls for a winged boy."
But from there, I go to setting. Setting comes before plot or character for me, because everything else springs forth from it. From the moment a character is born, where they live makes a mark on them. Nimira grew up in a place that was warm and beautiful, with gardens and misty mountains, surrounded by female dancers who valued beauty and pride, who loved men but mostly lived in a separate sphere from them. From there, she went to a farm, a family unit where everyone was expected to pitch in because livelihood depended on the sweet potato crop, the health of the goats, and such. If she had STARTED in the farm, she would value family and community a lot more, probably. She'd be more of a team player, less proud perhaps, but any artistic side of her nature would either have to be carved out selfishly, or incorporated into the group life--singing while she worked, or in the evenings with her family. She'd have different skills, different tastes.
And that's just the two places she lived within her home country of Tiansher.
From there, of course, she came to the Victorian-flavored world of Lorinar, dragging her background with her. Magic Under Glass takes place mostly in Hollin Parry's manor house, and to Nimira it will always be seen through the lens of places she has already been, especially the royal palace of Tiansher. In Magic Under Stone she is once again needed for manual labor, stuck in a big house with a lot to do and few people who can do it, so she thinks back more upon her time at her uncle's farm.
Every character in Magic Under Glass comes from a different background, subtly influencing everything they are. Hollin Parry, an only child growing up in a wealthy but cold home, wishing for the exotic life of his traveling uncle. Annalie, another only child but a dearly loved and petted one. Her parents emigrated to Lorinar before she was born, so while she was fascinated by travel just as Hollin was, it was not an escape for her, but more of a curiosity about the "old world". Karstor Greinfern himself came to Lorinar as a teenager and has a different cultural mindset. Erris, of course, is a fairy whose youth was spent romping in the woods with a pack of siblings and dogs; being jovial comes easy to him but being serious and emotionally open does not. He probably rarely had any time with his parents, tutors or what have you where he was alone and encouraged to talk about worries or fears.
Even in a contemporary novel set in America, setting and background have a huge effect on people. Culture in America varies hugely. Even cookie cutter neighborhoods vary. And the ethnic background of your character will influence them too. My German branch of the family has certainly left a huge mark on me, from my taste for intellectual matters to my love of sour-tasting cabbage based cuisine. And I'm also conscious of where I diverge from my background. I've never loved hiking, but boy, don't tell that to my German relatives... -_-;;
Where is your work-in-progress set? Where are your MCs roots? And what is your favorite book for setting and background? I suspect my preoccupation with it may come from L. M. Montgomery. Emily and those Murrays!