Arcane is simply exceptional. I can't praise it highly enough. Once in a blue moon, something beautiful happens. Things like new love, important personal discoveries, or, as it is in this case, "pure," beautiful artistry. To my utter shock and delight, Arcane is one of these things.
To put this in as clear a perspective as I can, I can imagine a future where someone visits the Musee d'Orsay in Paris and finds a Riot collection from the last couple years including Arcane only a few steps away from the Van Gogh rooms. It is that great. I'm willing to stake my reputation (lol) on this.
You don't need to know anything about League or the characters at all. The series is designed in such a way that anyone can watch it. All I'd recommend doing is watching at least the main trailer beforehand. Probably better to watch all the trailers (there are only a few of them), as they add to the experience in a way I've never seen before.
Please enjoy! <3