Here's how I do it:
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Step 1: Buy new champ / rework if I don't own them.
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Step 2: Load into a custom game, see if they can jungle. If so, continue clearing and practice ganking bots.
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Step 3: If they can't jungle (or after a successful jungle game), I play them in lane.
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Step 4: Play a norm or two (draft pick).
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Step 5: Go into ranked, and do as well as I do with any other champ.
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Step 6: Cry as they're banned 90% of the time until people pull their head out of their ass. (I never get to play Camille. Super fun to play, but permabanned. T_T)
Did that with Jhin, with Camille, with Warwick, with Taliyah, with Ekko, with all the releases since I've been playing. Sure I do better after a few more games, but I start out doing just fine and I actually have fun for a while. Hell, I got rank 7 Camille the day after her release I played her so much. xD
But, point is, this game isn't hard in the slightest. Once you know the general mechanics of the game, every champion is more or less the same thing, and pretty easy to pick up. Looking at their kit, you would know what matchups they would win, and what ones they would struggle in.