When faced with something you have to do, but don't know how to do, what DO you do? Maybe YouTube a how-to? Cause there are a metric crap ton of vids on any topic you can imagine (and a few you can't). There are arcane and amazingly useful channels out there. Then there are the videos that are clearly some desperate marketing 'guru' wanting to entice you into SPECIAL FOR YOU TODAY pricing on their amazing class that will teach you everything you ever needed to know about <insert topic, including writing, here>.
Some writers have channels that are legitimately helpful, but for writing mentorship, I lean on organizations. The single most cost effective way to learn about this industry while participating in the industry is to pay dues to RWA, SFWA, NINC, and other writer organizations that bring writers with all levels of experience together. Had I not found and joined RWA when I did, I'd still be out wandering in the novelist woods wondering why nothing was working.
Chapter meetings taught me the difference between
internal and external conflict. It was at meetings that I finally
figured out what voice was. When my first rejection letter came in, my chapter mates broke it down for me, explaining what the editor was
telling me and how encouraging that rejection actually was. Chapter meetings and local writer conferences led me to classes and to the people who's working style meshed with and enhanced my own. Do you know
how much that would cost if I'd tried to get that kind of support and
education from a single person? Far, far more than I had. Then or now.
Writer organizations give you access to an incredibly deep well of experience and information. I can go to the email loops or forums, ask literally any question and have germane answers within a day. All for the price of a membership. In that regard, I am super pro-mentorship. Take advantage of the organizations to which you belong and do what you can to give back, whether that's through serving on a board, or volunteering to stuff goodie bags at a conference.
It's vital to recognize, though, that mentorships have drawbacks. First, no one can do the work for you. Second, when anyone talks 'how to', you aren't getting The One True Way. You're getting the speaker's way. Whatever the teacher/speaker is sharing is what works for them. It may not work for you. When you're the one learning, it pays to keep in mind that you're going to classes in order to try out tools to see how or whether they fit your hand. When you find what fits, seek out that instructor and take every last one of their classes. The point is to take what fits and chuck the rest. In that way, you become your own best mentor.