If we are talking about content you can find plenty of advice here or elsewhere. But do yourself a favor and pay a tutor and/or find a study group. As in writing, dancing, etc. you cannot evaluate your own work good enough.
You will not improve your math watching youtube videos and reading books. You need to produce stuff that pass the "sniff test" to your colleagues.
You will not improve your math watching youtube videos and reading books. You need to produce stuff that pass the "sniff test" to your colleagues.