Poker Starting to study

Hi all,
I have recently began to take my poker more seriously as opposed to just playing for fun, I have had some success and I'd say my poker has improved quite a lot. Ive cashed a reasonable amount of tournaments including three wins. I know the only way for me to start getting more consistent results and make myself a more profitable player is to start studying more, I read some articles online about situations I know I need to improve on and I watch quite a few youtube videos about certain spots. I realise this can only get me so far and I know I need to start doing some more structured studying. My question is where to start doing this and how do I structure this better. I know one area I need to improve on is putting my opponents on ranges as opposed to a single hand, how would you advise that I start improving on this in a structured way?
Thanks for your reply and sorry for the long winded question.

(In a less long winded way my question is how and where do I start to study?)

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