Pick something that you're really good at and can carry as hard as one can. Like 1v5.
Like Tryndamere, Amumu, Maokai.
Never pick something that depends on other people to snowball. Else you'll never get out of silver :/
I'd say this is neither entirely true or false. I climbed pretty much all on my own to platinum in like my first 50 games on my smurf account playing exclusively Sejuani, who's hardly a carry or a snowbally champions by standard definitions, and I was building full tank, unlike some youtubers lately who have been going full AP (mostly for the lulz, but it does work if you get ahead).
What I've found has been the general winning recipe to climb the ladder (at least for me) was:
1- Leading your team at all times, always taking objectives when possible. You have to make the calls and properly evaluate what to do.
Watching LCS games or some youtube players will help tremendously. Trick2G for example, for all the crap he gets, actually gives solid advice on how to pressure the game and take objectives, often winning when his team is far down on kills or even with gold deficits, problem is stupid kids watch his videos and all they focus on is on how he spends most of the early game farming (which he only started doing because of feral flare and because Udyr is a somewhat mediocre ganker).
2- Playing a hero who's capable of initiating. I'd say this is pretty importante because teamfights win games and proper initiation can give a weaker team the momentum they need to win out a teamfight. Ults that punish poor positioning are specially good on lower elos, as ADCs will so often try to poke your team down before an engagement, exposing themselves. Being able to initiate is also important to prevent being initiated on, and to prevent the enemy team from poking you down before fighting. Having to rely on someone else to initiate is bad, and having nobody to initiate is even worse (if this is the case I'd suggest avoiding teamfights unless your team is ahead - just control vision and keep split pushing).
3- Vision control. Always ward the most important objective at the time, and ALWAYS have a pink ward on the map. Seriously, I don't care if you're even the ADC, t's 100 gold for vision that will often last several minutes, stop being selfish and buy one as early as your first back and keep replacing it when it gets taken out.
4- Stop making obvious mistakes, e.g. trying to defend a tower alone against 4 people, taking a stroll alone out of your base with no vision of the enemy team, trying to save a teammate who got caught out (let the fucker die), not stopping baron to kill their jungler who's right beside it to steal it or just teamfighting it out before continuing if you have a lead - if you don't, just leave.
5- Don't rage or lose hope just because someone on your team is feeding.
I'd say this all comes down to "game sense". If you do all of the above you will climb even if you're mechanically a mediocre player, regardless of position played. I have a friend who's well on his way to diamond and he mains support (plays it like 90% of his games). And I know there are no excuses because on my previous account I'd make the exact same complaints that most of you guys are making.
