I like to break down games into 5 types:
Type 5: 20% of the time the enemy team is way better than your team (this includes games with feeders/trolls on your team.) These games are pretty much automatic losses.
Type 4: 20% of the time the enemy team is, on average, better than your team. In these games the only way you win is if you absolutely hard carry the game (i.e. high cs, high KDA, high kill participation, high number of objectives destroyed.)
Type 3: 20% of the time the teams are evenly matched. Whether or not you win these games is dependent upon whether you play better or worse than the average person at your elo.
Type 2: 20% of the time your team is, on average, better than the enemy team. In these games you just have to play smart and you'll win (i.e. not suicide, flame your team, throw at baron, etc.)
Type 1: 20% of the time your team is way better than the enemy team (this includes games with feeders/troll on the enemy team.) These games are pretty much automatic wins as long as you don't troll/afk.
If you win all of your Type 1 and Type 2 games that puts you automatically at a 40% win rate. Next, if you win the majority of your Type 3 games that will put you above a 50% win rate and you will climb. The reason why so many people have difficulty climbing is they go on tilt after losing a Type 4 or Type 5 game and they carry that anger into subsequent games, play worse than normal, and lose a Type 1, Type 2, or Type 3 game that they could have won had they not been on tilt.