You don’t decide on your personal voice.
Your personal voice is the outcome of a million decisions. Or a handful of decisions, made over and over again, until patterns emerge.
The patterns reflect your preferences, your outlook, your insights. And when the patterns become well-established, you discover you have a personal voice.
You can’t really cheat on the million decisions. You can adopt someone else’s voice, and imitation can be successful. But a personal voice comes from time and decisions.