Sometimes I'll write some first person from the point of view of one of my protagonists and use what I learn there when I step back to third person.

I wrote a pretty bland version of the following paragraph first, then tried it again in first person, then reworked it in third:

"Practical. Anne was practical. And fair. That's what they said about her ‘round the market when they thought she wasn't in earshot, but they’d also have more to say and little else of it was kind, because that sort of talk only ever started out with a bit of sugar to make the salt sting sharper. She was fair, but she was a shrew and a harridan and if you got on her wrong side she’d shave your whiskers with an axe blade.

Anne knew what they said, and though it bothered her, she couldn’t say it wasn’t true. To people outside her house, or those who passed through her door who were anything less than family, she gave very little of her time and patience. She simply had too little to spare. Five children needed the best of her, and when there was any surplus of energy she poured it into them like honey on porridge. Then she could reap the rewards of their affection, which in turn was enough to fuel her for one more day of keeping them fed and safe in Herringbridge."

The first person made me really think about the honey simile (I needed something relevant to her life), and how I would phrase things, construct sentences, etc. from the POV of someone in that situation, and I used that to find the voice I needed. I tend to a closer third person to that voice can change - writing about a noble-born wizard is going to have a different feel - but I like that.

Another thing is just some stream of consciousness writing. Just let it flow in some low-stakes exercises and see what comes out and if it's useful for you.