Try putting on relaxing music or ambient noise while you play. It might help you de-stress.
If you find yourself getting tilted, stop playing League, or at least stop playing that game mode. Play a less stressful mode like Co-op, ARAM, or a RGM. You could also experiment around in Practice Tool, which might be therapeutic, or you could drop League altogether. Play a PvE game, work out, take a walk, meditate, etc, until you're untilted. Then you can keep playing.
Try walking in your teammates' shoes. I think it's harder to be angry at a person when you can imagine yourself as that person.
If you're toxic to trolls, then realize that they're winning. They want you to be toxic to them so you get chat restricted and banned. Keep yourself above them by not responding to people who are toxic to you first. Muting does help a lot in these circumstances.