I know some of them are not intent to feed. They are just sort behind or not good in early game. However, some of the players are so stupid to talk to. They just keep doing the same thing and die in the same place again and again. 
The only thing you can do is tell them to play safe but even then, people overextend in their lanes and expect not to die when they dont ward for shit and listen
You cannot really expect anything more than mentioning to play safer and making sure you ping when you notice danger (not spam ping as human psychology says you will incite them to ignore you if you spam ping).
However do not expect that this will prevent them from feeding. This is just all you can really do.
When people get frustrated they feed. How many hours of study and play does it take to get good at the game ?. Seriously, Riot pretty much does nothing to help players learn about the game's team compositions. Riot relies on players to teach themselves how to play and changes the balance of the game so that if you do get to have a chance to learn a champ this month then next month your learning again.
Add more champs+Change game setting=constant studying the game in order to get anywhere.
More effort should be put into the ability to tell players, when in Pick/Ban phase, which player comp are better or worse based on Enemy's picks/bans.
tell them to git gud and flame them on every mistake while calling for reports in /All chat.
works 100%
These champions are bad at not dying. They're immobile and not that strong early. Often a faster and stronger laner, or jungle pressure, will cause these guys to either miss every single minion, or die.
