Well, my instance Beehaw has a lot of general-use communities, so I spend some time in most of those, however, on lemmy.ml, there's a lot of similar communities to the subreddits that I followed back when I was using Reddit (e.g. Programmer Humor, Nintendo, etc), and I've also found some other cool communities that I thought were interesting. I basically just scrolled through Lemmy.ml's community list and subscribed to what looked cool.