Knowing your play style is key to finding a champion that suits you. How to find the champion that suits your play style?
After you have found the role you are the best at you need to find the champion you are the best with, this process is just like the last one but may take longer because there are so many champions. League of legends is constantly making more champions or changing the existing ones, by "nerfing" them or "buffing" them and sometimes they completely change the champion.
What i mean by "play style" is, are you someone who likes to sit in the back line or someone who likes to start the fights/engage. Once you've found the role that you're the best at that should give you an idea of your play style. Example if you like ADC/Marksman you'll be the type that likes to sit in the back line. This doesn't mean you can't start the fights but as a carry role it's your job not to get "caught" and if you start the fight 9/10 you will caught and get killed first.
So for most top lane champions, Jungler champions and some support champions they're the front line meaning they're the tanks/engage on your team if you fall in this category that means you are more of an aggressive play style. For the ADC/marksman champions, mid lane champions, and some support champions they're the back line meaning they're the "damage" on your team if you fall in this category that means you are more passive play style. Note that it's just a play style for the role that you've picked but the champion has its own play style, example some champions are fighters and some are assassins.
Once you've found the play style that suits you, then you need to find the champion that suits your play style. This is a key step for finding a champion that you will "main"/play the most often, keep in mind like the position, you need a backup champion in cases he or she is picked. Example in rank there are ban picks at the start of the game that make it so the champion is unavailable to pick or someone else picks the champion before you, this means you should at least have 3 champions that you're good with. Always try to play the champion you're the best with by doing so you'll be able to master your champion and will have a better chance of winning games.
Note: I put supports in both categories because some supports are part of the back line and some are part of the front line. Example Leona, Thresh, Braum are part of the front line/engage and Soraka, Nami, Janna are part of the back line/pock.