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 (click the badge for more info): https://lemmy.ca/post/5635462
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 :)