Earlier this spring, I taught an 8-week course on practical skills for using AI for nonprofits and churches. One major theme that got a lot of traction and I'm still getting questions about was how I use personas whenever I write.
Personas describe who I am, how I communicate, phrases, what to say/not to say, tone of voice, etc., for each domain of work I engage in. So I have personas for my day job, my brands I'm working on, and even one for communicating to my wife.
I typically create a project for each domain of work, upload the persona to that project, and in the project instructions, tell Claude to use that persona whenever writing in that project.
I've uploaded a couple of those personas here in the chat, if that's helpful to you.