Your team is your enemy
There are a lot of people on here who think that your team is your greatest ally, and that a little bit of positive thinking will let you win every game. These people are delusional. Ignoring the fact that every game has to have one winner and one loser, and ideally everyone's win rate should be 50/50, your team is far, far more likely to antagonize you than your opponent.
During champion select, your opponents cannot completely screw over your team from step one by hard countering themselves and autolocking a role that has already been filled...twice. Your team can.
Your opponents cannot steal your CS when you go to clear a minion wave. Your team can.
Your opponents usually isn't the one putting you down for every single mistake. Your team is.
Your opponents, generally, can be expected to be working with a single goal in mind that you can work around: They want to win. Your teammates...well I guess they're having fun dancing in the jungle or something. Good for them.
Your team is quite frequently going to be a ball and chain, refusing to cooperate with reasonable suggestions and taking offense at any sort of comment or criticism...even if they've been ripping you a new one. Your opponents, at the very least, are going to be generous enough to say "gg" at the end of the game, even if it wasn't, under any definition, a good game.
So just remember. The greatest obstacle you will ever have in climbing the ranks is your team, because one bad placement got you stuck with paste eating thirteen year olds who, despite staggering through their ABC's and apparently not having any hands to manipulate the mouse with, managed to install and log in to League of Legends.
See you all in ELO Hell.