Was a lot of it classic word of mouth, email, etc.?
I imagine something like that, but I’m wondering as I feel like there may be some useful pieces of knowledge that may be worth recalling as people gradually start to move back out of the more centralized sites/services.
Usually it meant finding websites with similar interests and banding together. You might form a webring, or trade banners with an affiliate site, or have community-voted top 100 lists, etc.
In 2000 I had a website about the then-current animated series X-Men Evolution, and I remember getting emails from other people who ran X-Men Evolution fansites and we would link back to each other. Eventually enough X-Men Evolution websites sprung up that one of those Top 100 list pages* sprung up to rank all of us. Clicking on my banner would result in a vote for me. I don’t think I was ever the #1 page, but I remember being in the top 5-10.
*if you have no idea what I’m talking about or are too young to remember these, they were EVERYWHERE in the early 2000s for many different subjects and fandoms. I don’t really miss the era of the Top 100 lists, because they could be easily gamed just like SEO (emulation sites were notorious for this). But I spent many hours of my teenage summer vacations finding a subject matter I liked, like Pokémon, and just going down the list and exploring.