To earn a champion rating you need to perform the best out of your team. You also need to win the game. Champion status is only given to a player on the winning team. By playing a few games you will learn various tips and trickes that will help you crush your foes.
Simply by playing enough games and performing well in them will quickly earn you this achieve :)
Also by winning head to head (1v1) matches you automatically get the champion status as you are the only person on that team! ;)