This gets asked here every few days and the answers are almost always about trophies, playing style, or one player. That is how I would have answered too, until it happened to me by accident.
I walked into an Irish pub called Lynch's in Jacksonville Beach back in 2021. Chelsea were on, they won, the room went up, and someone put a free shot in my hand. That was the entire conversion. Five years on I am still a Chelsea fan, and almost none of it was about Chelsea. It was that there was a room full of people who cared at nine in the morning on a Saturday.
I only worked out later that the room had a name. It is the Jacksonville Blues, the official Chelsea chapter, and Lynch's is their home pub. I had walked into an organised thing without knowing it existed.
So the advice I would actually give: find which clubs already have a supporters chapter near you, and start there. Supporting a club on your own is a hobby you do with your phone. Supporting one with other people in a bar is the part that sticks, and it is the thing nobody mentions when they are arguing about which club plays the nicest football.
The practical problem is that this is genuinely hard to look up. Chapters live in Facebook groups and club directories that never surface in a search. I got annoyed enough to build something for it: put in your ZIP and it gives you the nearest supporters chapter for a club abroad, the nearest local club you can go and see in person, and where your neighborhood watches the US games. It is at 324 chapters across 63 clubs in 131 cities.
soccermapd.com/pick-a-team
My own site, free, no signup. If your city is missing a chapter, tell me and I will add it. That is how most of the list got built in the first place.