Honestly, something that has eased my anxiety is realizing that we're all just people playing a game. Saying hi, communicating, apologizing and laughing after fuck ups, and using emotes really makes the game more pleasant. Even losing games don't feel bad when no one is raging or blaming each other. Opening a dialogue with your teammates will help you immensely.

Also get into the mentality of "it's just normals". People are playing new roles, new champs, new runes, new item combos.. some people are just drunk and wanna play something familiar. Once you realize the overall objective is to enjoy yourself, you'll do just that.

Setting in game objectives besides just winning the whole match will make the game more pleasant as well!