If you don't know what you should be looking for then it's easier to read up on it and then learn to actually implement it into your playstyle rather than discovering it which can take foerver.
To be honest, almost every guide I've ever read for League was bad. Even the guides written by very strong players don't necessarily do a great job of communicating the stuff you need to know about a champion.
To start learning a champion I think you mostly need to know two things:
* What the purpose of this champion is in the game. Like, what are you good at? What's your win condition? What should you be building most of the time to do those things?
* The super basic vanilla play pattern for the champion. Almost every champion has one or two straightforward interaction patterns that they apply, which flow naturally out of their abilities, and then the rest of the game is mostly learning variations on that basic pattern.
Examples:
* Renekton's E->W->Q->E.
* Syndra's E->Q->R.
* Alistar's W->Q or Q->W.
* Caitlyn's trap->auto->Q. (Not a perfect example but I'm bad at ADCs.)
You can probably just figure out the play pattern in game but it can be nice to know it beforehand because you're going to execute it like a hundred times so you may as well learn it.
Once you know that stuff the rest is just, like, a hundred years of tiny details.