Unlike some other people I think that using "mute all" isn't a good idea, because there are still good people playing LoL and that will want to message you simply to be friendly (saying "wp" or "need help ?" or something), or trying to give you advice.
And sometimes there can also be -friendly- banter, totally different from flaming, which can actually make the game even more fun.
For example, I never flame people unless they flame first (and even then I generally just mute and report), and when I see someone struggle or make mistakes that may cost us the game I simply point it out in the most polite and friendly manner I can. And if they ignore me, I just don't mention it anymore - some people don't want to improve and just want to relax, and I'm completely fine with that.
And when I see someone being flamed at, I tell them to mute the offender, and I think some people feel relieved that at least someone in their game (I also say it to people on the enemy team) is friendly, so you would also be missing out on that.
So yeah, just mute people the second they show the tiniest hint of toxicity. And mute their signals and emotes too ! Those are normally very important since it's a team-based game, but I found that toxic people care more about flaming than winning, and so they'll spam signals for stupid reasons.
It's a shame you're playing on NA, I would have added you, I actually am looking for beginners to play with and that share my "zero-tolerance for toxicity" policy.
**TL;DR: don't mute all because you're missing out on friendly chat and advice. Mute someone the first time he says something you don't like. And when you do, don't just mute chat, mute signals and emotes too. **
