I have over 6k normal games, I am extremely experienced playing normals. Normals definitely make you a better player over time. I started ranked play after getting bored in normal games and I wanted to be rewarded for my game play ie: season rewards,badges,etc. I quickly advanced from silver tier to gold after a while. I was so happy that I hit gold division 1 and was able to get a free skin at the end of the season. The next season, I aimed for gold again, got it, was happy. Then came the current season, I knew I could hit gold 1 again, I got there, then yesterday for the first time I achieved platinum.
All those games I played in normals really set my mind to "how to win", so it's good practice. But, ranked games are where it's at. More pressure, better players and better plays. Overall if you want to become better at the game, you must play ranked, and literally nothing but ranked. I main jungle, then top, support,mid. I never adc, which might sound strange, but I hate that role. I make sure my team knows I pref jungle and can't adc to save myself. So pick your most favorite role, and have at least two favorite champions for each lane. Spam those champs, become known for playing specifically top lane wukong or jungle udyr, etc.
Now comes the carrying part. Imo, the best lane to carry from is the jungle. So that's where I started at, amumu,warwick,volibear,skarner back in season 3. These champs got me gold, and my experience in the jungle from all the normal matches helped. Times changed, those champs aren't my favorite anymore, and been nerfed, but are still okay picks. I tend to stick with champs that don't require skill shots, and have the easiest skills for ganking/team fighting. I've played so much jungle games, that I'm just insanely comfortable doing it all the time.
My last advice is to spam teambuilder as much as possible until you have very high win ratio with a specific role and your favorite champion. Then switch to another role, rinse wash and repeat. Now you are ready for ranked. You don't have to be best in every lane, there are many one trick ponies out there in challenger. Lastly, watch the pros, not just from NA, I mainly watch korean videos and guides. Their tactics aren't popular over here yet, and it gives you a slight advantage in game when most people here watch NA/EU games, and are clueless about korean builds and playstyles.