A long time ago, I was struggling with the issue of third or first person. The way I solved it was very simple: I wrote the same scene in both, then compared. Third person worked best for my intent, theme, and tone.
Choosing a viewpoint character works much the same. It’s best if you don’t have too many candidates, unless you really want a lot of practise free-writing. It’s also a good idea to decide on the viewpoint itself first.
You can utilise writing exercises or prompts to write your comparison pieces, but it might be better to write out a scene or idea you already have in mind for the story.
The dusty scent of rare editions clung to Aurelius’s hair and shoulders like the clutch of a jealous lover. He turned a page with one hand, fiddling with his wire-framed glasses in the other hand.
Neither hand shook, but anyone who knew him well could have seen his anxiety. Sadly, no one knew him well.
Pulsing lights and loud noises were part of Mazary’s everyday life. Unfortunately for her, they were less literal in the mornings, and far less enjoyable.
She flopped across the kitchen table in a beautiful display of self-pity. Her arm struck her coffee cup, sending it toppling over the edge. The crash made her jump.
In a few hours, she would transform from a human wince with a hangover into a mafia princess. She did it every day.
But that was still a few hours away.
Winded and drenched in sweat, Simon skidded around a corner. Her fingers scraped on the brick as she pulled herself up against the alley wall.
Her heart jackhammered in her chest, threatening to snap her ribs from the inside.
An army of shiny black shoes thundered past. But one pair lagged behind. Uncertain.
Simon knelt to draw a knife from her boot.
Still not sure, but I think I have the most fun with Simon. That seems as important a factor as what serves the story.