I dare say URF games are more serious than promos and even the LCS itself. You need to strictly follow the meta and pick one of the 10 champions Brofresco made a video about. And you are not allowed to break the meta. Or else report!
And don't even try to experiment or "have fun". NO FUN ALLOWED! This is a very very VEEEERY competitive game and wining or losing is life defining. If you are playing with 4 other premades on your team and you fail to obey them when they tell you to go to a certain lane or to pick a specific champion, or even if you make the sliiiiiiiiiiiiiiiightest mistake, the four premades will immediately take it all out on you. You will most likely suffer third degree burns from all the flame you recieve. And don't even try to defend yourself. Remember, premades DO NOT make mistakes. Everything they do is a part of the strategical master plan they have created on Skype. You cannot question it.
Did i mention if you lose a game with 4 premades on your team it will be your fault?