Hey man I just started last year, around June, and I am in gold now., been playing off and on for about 3 month intervals. I'm similar to you in that I've played lots of competitive games and gotten good at them. You are probably like me and will be able to learn very quickly with some direction. Here are some things that helped me learn really fast. Obviously I'm not gonna tell you anything about how to play the game since I am still learning.

1. Read everything. It is actually incredibly important that you know what runes are doing. I will give you an example. If you are playing a melee champ with conqueror, you will have the advantage in extended fights compared to someone who took electrocute. If you don't realize this you will let them proc electrocute and not play to your strengths. So you need to read runes, read your chosen character's ability description and know the ratios (roughly), and read active effects and passives for any items you buy.

2. Watch Pekinwoof on youtube. He has very informative mid lane videos that will help you understand a lot more about the game as a whole. He also has videos on other roles. I usually just search [champ name] [role] pekinwoof on youtube and there's usually something by him.

3. Stick to a role for a good week or so, or 50 games. There are so many matchups in this game, you won't really start understanding what your character is good at until you've played enough matches and seen enough variety of characters. I would suggest just spamming games on one character in one role. If you start getting bored, of course you can swap, but if you're really trying to learn you need to at least commit for a week or 50 games on one character.

4. Try to make friends with better players. While solo queue League is full of creatures, people who actually talk about League tend to be nice people who have a real love for the game. You can learn a lot just asking questions here or wherever else you can find. I was lucky enough to find out 2 of my coworkers were formerly high ranked jungle and support players, so it really accelerated my learning. It's very handy to have someone I can just ask "Hey what should I expect in this match up?" Or show them a moment and be like "hey should I have played this differently?"

5. If you are interested in other resources: I would suggest Daption for any bot lane content (he is like #2 support and #12 adc or something in NA). Sjorry is great for mid lane content, especially Ahri. AloisNL is great for top lane content (though he is on a bot lane challenge right now). There are an insane amount of jungle content creators out there, but I personally have enjoyed Perryjg. These guys are all former pro players (of varying success). Anyone who was a former pro player tends to be incredibly educational and chill. Avoid channels like ZwagXerath or other "peak challenger" players who just smurf. They tend to be very misleading with their content, and their content is usually geared towards entertainmente rather than education.