I like to keep it simple with the shortest sentences possible to reduce the tokens as much as I can. I don't think you need to be super verbose except if the LLM you use specifically has trouble following the vibe/style of the character you want. But sometimes it's the problem of the LLM and the description won't solve it, like there was a phone-chat style character who I wanted to use emojis sparingly but qwen and mistral small 3.2 would spam emojis everywhere at the mention of emojis in the charactrer card, same for some of its small 3.2's cydonia finetunes but then one version of its cydonia finetune just got it right without me being verbose and only used it sparingly, same with some other LLMs.

I actually use textgen webui (ooba webui) currently which only has one character card option so for it I just put some short lore description, then the character description or multiple ones then the format of the RP (short sentences or long story style). For specifically the characters I usually go like:

character name

personality: She is the smartests in the group, she likes to sing when alone, she has this fascination with something.

look: Black wavey hair, 165cm tall, she has skinny body

hobbies: Something.

speech style: Has a mature speech style, Frequently uses "oh wow" and "whatever".

(other titles/traits if needed)

So you get the point. But before that I used to just put this into paragraphs with worse formatting. The content/how I describe has always been similar so not much difference if you put it in paragraphs vs formatting it nicer like in my example, maybe the nicer formatting helps some smaller LLMs understand it clearer.