A while back I was going over some notes on characterization and writing as a character, even in the third person perspective (writing as if the book was a collaborative process between the characters of the book, each one writing their own paragraph).
I came up with a small test to check if I'm in the mindset of the character: The orange test.
Have your character describe an orange, or, write an orange into a scene as if it was your character writing that section. If there's no scene, nothing to write, writer's block... write about an orange.
Here are three characters from my completed manuscript, Agape:
The small round thing on the counter was spongy. The outside was hard, glossy and firm under fingernail. It smelled good, like cleaning solution used in the kitchen. Tapping it produces a thud with a slight higher pitch on the outer shell. The firm outer part hides a sponginess inside. It looks like it should feel spiky, maybe, with little hairs in the pits, but maybe not. Pressing a thumb in breaks through the skin and more of the neat scent leaks out with a sticky liquid. It has a white fiber, like string from my shirt, now fraying off it. The liquid tastes good. Opening it may be difficult.
Another:
The orange was pitted gently, with a texture like a golfball. Bram sees the micropitting around the edges, and the sheen of natural wax coating. Round, abnormally so, on the hard table, it sits alone on the marble.
A third:
The orange ball was on the table. The juice is sticky. It's hard to open and there's nothing good inside it. It smells nice when it opens, but then it gets all sticky. There's nothing else on the table.
Neither of these have to be stellar, only a quick scratchpad to get in the character's mindset, whether someone who had never seen a fresh fruit before or someone who doesn't want to eat the orange. The orange can be in a cabinet, on the floor, on a tree... the scene doesn't matter as much as how your character describes it or lives in it.
You could even use it as a seed for anything else you could imagine, a character distracted and flitting from subject to subject in another case, setting the orange as a starting point as a simple picture on a carton before spiraling into distracted thoughts and scenes down the way. The importance is in connecting with the experience of your intended character.
Write it, look at it, ask a friend if they can identify which character is which based solely on the text, vocabulary, tone, sentence structure, even punctuation and abbreviation (if you don't have a name in the text like mine above). If it doesn't work, try again. It's not like it's a major scene (unless you find that thread to pull to make it one).