I play since 2010 and never got a ban or warn. Except an auto-mail for disconnecting (my internet randomly fall and don't go back).
I think that if you just treat other like you want themt o treat you, things go smooth.
Instead of raging at your mates, try to organize them. Respect them and they will often respect you.
Instead of raging, flaming and calling someone "noob" because of a odd build, try to talk with that person and offer suggestions (maybe he don't know much about the mechanics or is new to the champ).
In the end, respect your team mates and respect your foes. After all, we all are partners in that great game and we all seek fun.
For you guys who got warned or banned once:
Really, try that. Try to offer a hand to players. Even lvl 30 players as some of them reach there playing only bots. You may not regret it.
Last time I logged a player I helped since below level 20 (I didn't even remembered him, I am bad with names and help many players), and now level 30 with many games played, sent a message to me thanking for the help and said that now he was playing really better and is having more fun.
That single message changed my day.