People need to be explained how to play each position
When you see kids playing sports in high school or pros on TV, they all at some point were basically sat down (not literally, but over time) and explained by older, or more experienced players or coaches how different positions are played in order to win.
In league, players just show up. Riot doesn't give them any base line of knowledge.
Things such as "we know its tempting to build more AP items as a support, but over the long run vision produces more wins. Wards kill enemy champions, and you need not be so worried about your damage output as you should be with keeping your marksman alive, which includes making sure he or she doens't walk into a blind jungle and get picked off.
This should be done in tutorial vidoes so people actually watch them.
Honestly, I think it should be mandatory. No one shows up on a sports field with no basic concepts of the game ready to have other players pit their standing and rank off of how good this player does.
Its fucking absurd. Educate the god damn players Riot.