Heya,
I rarely post, and when I do it's usually wordy. But hopefully I can give some good advice, so here goes.
I only returned to league recently, and carried myself to platinum with only enchanter supports and a 74% win rate on Janna. Back in the days I was mid-plat as well, and carried a second account to platinum playing only the lowest win-rate champions, primarily pre-rework Urgot.
As such I'd state that champion picks aren't everything. It's a factor and you should look into, but it's not the be all and end all. Despite that, a champion that is relatively weak at the moment and also relies heavily on your team mates (Ivern~) is not really recommended. It's doable for sure, but you are making things more difficult for yourself.
Consistency over risk
My own experience in silver and low gold is that people are very focused on making kills. They play overly aggressive, often to their own detriment. Maybe they got fed some time and hope to repeat that, maybe they underestimate their opponent. In either case, a simple way of winning lanes in silver league is often to sit back, out farm your opponent, and punish them when they make a mistake. I know this isn't really the same for a jungler, but the point is try to punish your opponents mistakes rather than forcing situations yourself. Taking a risk is a 50-50 of who comes out ahead. Consistently out farming your opponent and taking small advantages will always get you ahead.
I'm not saying you shouldn't try get kills, but pick your fights, and not all fights are to the death. Trading 1 for 1 is often worse than simply making your opponents recall, and not dying is often worth more than getting a kill. Forcing the enemy back and getting drake is better and safer than tower diving and losing your jungler in the process. Not just that, but the amount of times people aren't on the same page, one person dives and the other doesn't; and I have to watch them ping question marks at each other for the next 30 minutes...
Wards save lives!
It seems obvious, I know. But knowing where the opponent is not only prevents you from getting jumped, but also help you catch out opponents and grabbing a safe advantage. Not just that, but it helps with taking objectives; which is like half the game at the moment. Make sure you always have a control-ward on the map, and carry an extra (to de-ward dragon, for example). In addition, keep using your yellow trinket; not just at random but think ahead of what positions are important to keep an eye on at that point in time.
Master a champion without bells and whistles
People often say Twisted Fate is the best champion to learn the game on. The reason for this is that Twisted Fate doesn't have any gimmicks to rely on, and instead 'forces' you to master the game's basics before you can have success on the champion. He's squishy and has no mobility, so you have to learn positioning. His damage relies on a slow skill-shot and slow telegraphed stun, and he can't really burst people unless fed, so you have to learn to poke and trade. Meanwhile the only 'special trick' he has requires you to watch the map and play with vision.
Now I'm not saying "go play TF or stay bronze", but make sure you get these things down before relying on Evelynn stealth, Rengo one-shots, wind walls, 50 dashes and a flash to win.
Be willing to get carried
There's plenty of games where you don't do well, for any reason. It's tempting to try to snipe kills and take risks in an attempt to make a comeback and prove you're iron4 everyone is labeling you as. Instead, be willing to build more defensive and help making the lives better for those who are doing well. Do what you can to let the one who can carry do their thing and let them else take the spotlight.
Don't be a Riven
Again, obvious... but don't flame, don't ping spam, don't make snarky remarks, etc. It just makes people annoyed and unfocused; it lowers team morale and makes people dislike you. Toxic people generally get a lower priority on my shields and trying to save them (both unconsciously and consciously), and I've lost count of the amount of games won after a few simple words of encouragement.
That's all that comes to mind at the moment. There's weren't aimed specifically at you, more as general good things to keep in mind. Hope it helps. :)
