Any advice you can give to a newbie when it comes to ranked? Things like good leads, matchups, etc.?

I'm not gonna hear anyone say "Just avoid ranked", because I am not going to listen. I really love this game, and I'm willing to grind ranked, but after losing so many times, I think it's time I ask for advice.

I was very excited going into this ranked season because I got a lot of great cards. I copied the meta decks exactly, like Mega Blaziken/Heatmor, Mega Absol/Hydreigon, Mega Altaria, and Suicune/Greninja. But recently, I've been getting my ass kicked by many older decks. I got obliterated by a lot of decks I didn't even know existed.

I've been seeing so many posts of people going on 12 game winning streaks or getting to the top of master ball in one day, and I'm honestly wondering how the heck did they do so well, while I'm using a very similar deck, but I'm losing all the time. This game isn't really that hard, is it? From my experience, there isn't that much skill outside of knowing what cards to use at the right time and stuff like that. I know it's definitely because of their experience, but I think it goes beyond that. I think there's something genuinely wrong with the way I play that costs me games. I don't know what it is, but maybe it does exist. Is it because I'm constantly changing the decks I want to use?

I genuinely want to ask for advice. Honestly, any bit of helpful advice will do. Things like knowing when to use your Oaks or Copycats, what makes a good lead, what to do in a bad matchup, etc., teach me anything that can help me grasp this game better.

Any helpful advice will do. Thank you very much!