Check out https://browse.feddit.de/ for a central place to find popular communities, or go to “all” and switch to “hot” - that’s how I’ve been doing it!

You could join New Communities and have a whiz through there to try and discover some.

EDIT - forgot the link! https://lemmy.world/c/newcommunities

Failing that, what sort of things are you interested in? Music, films, politics, art, food, etc?

Also, shameless plug, here’s a couple I’ve set up:

• https://lemmy.world/c/mst3k
• https://lemmy.world/c/arresteddevelopment

Have a look at https://lemmy.blahaj.zone/post/61827. It’s not strictly a list of communities, but it’s a guide on community discovery that should help you get started finding communities on your own.