Warning, I am NOT a very high leveled or super skilled League player. All I am doing here is just giving basic and general advices.
Speaking of which, here is the start of this guideline:
Dedication: 
As for starters, no matter how long it takes you to become better, be prepared to spend a lot of time and especially a lot of patience. If you can handle the stress from failures regarding yourself and those belonging to your teammates, then you are all set into the path of becoming a better player and maybe a god like carry. Be advised that efficient time usage in learning is better than just being frustrated about being bad or something else than learning and training for a long period of time. When you really want to learn about a something, experience it. Watch pros or those who know the champions in streams. Do not just stick to one information source. Be open minded about learning stuff. Always be curious. Mechanical skills are something that you need to dedicate, whether you want to to carry or be better.
- Learn and Understand about yourself
To carry a team, you must start to know how to be the carry.
Whether that is being a Top, Mid, Support, Jungle, Marksman or anything else that is out of the traditional NA meta, you must understand who and how you should play. Remember that every champion is unique. So maybe if you learn something specific about a champion, it may not be applicable a different one. For example, A thresh hook has a wind up animation to load and it does not immediately pull the target to you like a blitz hook. However, even with those differences in mind, some techniques and strategies that you learn will be persistent through out your gaming session; for example, learning how to aim skill shots, how to farm, how to ward, how to be aware of your map, when to gank, when to back, when to dive, who to focus, etc. It all depends on adapting everything to what you are playing. And so, I urge you to study the basics of the game back to start one. You said that you were bronze or what not, so it seems to be a good time to restart learning the fundamentals. Since I do not want to spend a lot of time on typing on every little things, go out and look for videos, streams and written guides if you want to learn about the fundamentals and the specific elements of that one role/champion that you want carry with. To be able to carry, you MUST fully understand the capability of your champion and apply it's maximum potential. That comes from countless learning, practicing and adapting. Theorically, you could become the master of any champion, but it is important to know that it is preferable to start learning a few champs and stick to them. It will be hard and will take more time to master a large variety of champions, but it is still possible.