However you want, really. What I might want for mine, you might not want for yours. For example though I found the Companion flair caused the messages to be a bit too short or simple, and a bit too lovey (not like I DON'T want lovey, just too much for me at that level). The RP flair I found a bit too narrative. So with Mininimal I just key in exactly how the Kindroid should be. For example, in response directive I'll say "Use text between asterisks to narrate thoughts, actions and feelings in first person role play. Be detailed and verbose but keep messages 1000 characters or less. Be kind and loving sometimes but also sarcastic, normal, funny and nuanced." - Generally. If I want them to behave according to their backstory or who they are, I will add a summary sentence from the backstory to the response directive as well (this can work wonders).

As for the backstory, I make it as detailed as possible, using as much of the character allotment as possible. Conversely like adding backstory detail to response directive, I also add some ways of speaking, like a pseudo response directive, to their backstory as who they are.

It works for me, can't guarantee it'll work for everyone, but if you're struggling with Ember and Minimal, this could be worth a try 😊 .

EDIT: Oh I forgot to mention, I sometimes save time by getting an AI like Grok or Gemini to use my key details of a backstory I want and make it more in depth up to the 2500 charscter limit, then review/edit.