I’ve been experimenting with this for the communities I help with!

See sidebars for some examples:

• !canada@lemmy.ca - using dropdowns to organize unwieldy lists
• !medicine@mander.xyz - a long rules section was required
• !newToLemmy@lemmy.ca, !communityPromo@lemmy.ca, !sockPuppetSociety@lemmy.ca for some shorter sidebars

I agree with the concise description, and I try to have that as the first thing in the sidebar. After that, I’m playing with the following, depending on how relevant each is:

• A badge showing the total subscriber count, like this: Image
  • I swap out the community name and play with the colors for each one
• Community rules, as concisely as possible
• Other helpful tips, little starter tips, etc.

I try to keep the sidebars clean and collapse as much info as I can. Here’s a guide to the markdown you can use.

If there’s something in one of the community sidebars that you want to replicate, let me know and I’ll share the direct source :)