I usually point people to Statuo's guide:
— https://rentry.co/statuobotmakie

I don't have a guide since I sometimes do things that are not conventionally accepted and may be criticized lol. LLM work well with plain written text, so you could write a paragraph simply, if the LLM is something smart like GPT-4 or Opus. Otherwise I'd recommend labeling sections (as you see in Statuo's guide). For example:

Name:
Likes:
Dislikes:
Goals:
Etc


Some things I personally do:

My bots don't have a format, it's more free flow. Suppose you write 5 paragraphs, then label the chunks of text. A good example is my bot Odette, where I broke her backstory into three sections: Backstory, Reunion with Mother, Acquiring the Brothel (I forget the exact wording).

Labeling sections help because it gives the LLM a "topic" to group by, otherwise statements are prone to multiple interpretations (for example, does "sadistic" refer to when dealing with enemies, or is it part of their personality? Huge difference. Complete sentences also work). You can also label a section literally anything you want. For example, Managing the people of Lestara: [text here]

Grouping and placement of sections is important. If you group similar sections of text together, the effect will be stronger. For example, I don't want to describe "Romance" behavior scattered throughout, I want to describe Romance + Sex all together, in adjacent sections. Or, if the character turns out to be too horny, you want to separate the sections.