Echoing sentiment already stated above--you probably won't really know if an FC is for you until you try it for a while, especially since it is different for everyone.

Do you want a group that is super social, and talking basically all the time (in text? on voice?)? Do you get annoyed by people randomly narrating their lives, or asking for handouts? How quick are you to perceive "cliques" and are you quick to make friends? Do you like when everyone says hi when you log in, or doesn't wait for goodbyes? Are you looking for regular events, or are you more of a go with the flow type? It more or less comes down to what level of social interaction you are looking for, and whether personalities mesh.

There are FCs of all kinds out there, so don't be afraid to try one for a little and duck out if it isn't quite what you're looking for. There's no point in staying if it isn't a good fit--this game is supposed to be fun for you, after all, and most don't mind departures anyway.

As for where to look, there's this forum, r/ffxivrecruitment on reddit, randomly shouting in any of the big cities, looking up the FC of someone you had a good interaction with.... I found mine on reddit, messaged the FC leader to try to get a feel for the group, and have no regrets. ^-^