Stop Hating On Your Teammates.
Seriously, no one on your team needs to hear about how useless everyone is. Just stop. Stop. No one gives a shit. Every single game of LoL all I hear about is how bad I am or someone on my team is.. THAT is what makes other people get pissed off and start raging back at you.. and players in the next game, and then the players in the game after that one. You are starting a never ending cycle of players being on edge with everyone on their team.
The next time you are tempted to start hating on that 0-5-0 Top laner or your support Blitzcrank who can't land 1 hook to save his life just close your chat box, take a deep breath, and tell yourself it doesn't matter... Because trust me, it really doesn't matter.
Being a shitty teammate doesn't help you win games, all it does it make everyone on your team hate you. So stop being that guy who thinks he's better than everyone and accept the fact that everyone does poorly sometimes because if your enemy never played poorly you would never win one single game.
Mistakes are made, bad things happen.. That doesn't mean it's okay for you to start bullying your teammates and making them feel like complete shit because they weren't able to carry you or make the play you think should have been made.