Many of us play an array of champions, and most of us do play them to a pretty good extent.
Now, what does mastering a champion mean? well in terms, knowing the champion inside out. From little combat tricks, to power spikes, and roles you should be fulfilling as the game progresses.
(MadCaster's whom I've seen make a good example of this)
We have people like Bryff who mains Irelia, or Hakubruh with Gangplank, who regardless of who they are up against, they seem to do good with their champion.
They have higher odds of winning their lanes due to knowing their champion's limitations, and possibly snowballing the game towards their favor.
How does one learn their champ? how do you "one trick" a champion?
well all I COULD say is play the champion a lot, it works but if you are play the champion with bad habits, those habits will limit you. So myself, only as a measly Gold V player, have found success in playing with the big boiz in diamond with these few tips.
1.) Theres a time and place to be aggressive: Some champions require you to play under tower and avoid fighting at time, until certain requirements are met. Riven for example ( as she's my main) can most of the time out bully anyone at level 1 if her combo is correctly executioned. Now, lets take a renekton match up for example, I can hypothetically stand in the top bush, waiting for him to start heading towards the CS, as riven my options are Auto-Q-Auto-Q-Auto-Q and disengage (notice i didn't fit in a last auto in there due to my last Q been a knock up effect, leaving room for me to escape without him trading back.) and his options are one of the two, if he starts Q then all he can do while I combo is Auto Q Auto. or if he starts E, which i believe is his stun, then he will be able to trade even with you, his option would be Auto-E-Auto-Auto. Now why would you fight someone at level 1 as riven? well riven is easily bullied out of lane without her cooldown, renekton is one of her weakest lanes, and by asserting dominance over renekton at level 1 you can hope to get OUT of laning face either even or ahead. Now if i were to play passive, Renekton been the bully he is, would either deny me CS or force me out of lane, hence setting me behind, at level 3 renekton has tons of kill potential, understanding this as riven you can avoid fighting him, wait for his cooldowns to go off and trade wisely.
2.) What does MY CHAMPION EVEN DO? Ever had that awkward moment when you didnt realize your champions extra abilities? For Riven, every time she use any ability, she gains a SHEEN like effect, empowering her next auto. I would suggest RE READING your champions passive and abilities. Lets say I didnt know any of my champions abilities, just the minimum. I could Q three times in a row as riven, and completely miss out on the empowered auto riven gains, allowing the enemy to out DPS me. Every second in a trade/fight matters, 10 HP can sometimes really be the difference, that one last auto that could have won you the trade and snowballed the lane.
3.) CS'ing can be brutal if you aren't accentuated with your champion. Just like trading blows, trading CS can mean the difference on whether you get that extra healing pot, or that armor cloth. Learning to properly wave clear is super essential towards winning. I'd suggest carefully watching every minion and keeping track on those that are 50% below health and see which minions are attacking who. Learning your champions auto range is pretty crucial on whether you can play against a lane bully. If you are ever in the flip side of doing the "Bullying" heres a quick video that will explain expert wave freezing:
(This does apply to every lane, not just top, but it is most commonly used in the top lane)
(SIDE NOTE: Sometimes even avoiding the lane on purpose can be a good way to play a losing match up, lets say renekton killed me in lane, i would go straight to bot, ping my jungler to come and have a 4 man gank, having my bot lane snowball, always look for those TP plays. Roaming can really go a long way, especially for midlaners.)
4.) Enjoy the champion you play, you will be playing with it for at least 20 minutes per game: Lets be honest, if you are Vayne, and you are getting one shot every time the enemy Zed decides to sneeze in your direction, and if you dont know when you are able to survive a fight, then most fight, you will most likely lose, champions like kog' Maw, it takes a few items to get rolling, you could be quite a few kills behind, but with the right items, you can get back into a game.
Most champions have dedicated threads on their match ups and builds.
I would suggest perhaps giving these a look and finding the one that aligns with your champion.
For Myself as a Riven Main: https://www.reddit.com/r/Rivenmains/
and Gangplank: https://www.reddit.com/r/gangplankmains/
Also watching what one trick streamers/pro players are doing helps out as well, so go check out some twitch content!
You are good enough! Learning a champion does take an amount of time no matter how simple or complex they are.
Hey hope this helps a little any questions please drop 'em here! and if you have any suggestions as well!