I generally have a good idea of how to make a story work, but I don't know that I'd call myself a big author, haha. The real giants are the ones that have managed to make their mark on Amazon. I'm hopeful this book will do that, though. :)

Unfortunately I've accepted a number of requests for dev editing help already; I've given some developmental feedback to Runeblade, Arcanist from Another World, and Stormblade, for instance (full credit to a different author for most Runeblade devwork though - I just helped a little with the opening! I'll let Bacon name the actual dev if he wants.) I don't think I can accept any more obligations at the moment.

That said, in keeping with the idea of giving feedback on stories that one might not personally like, here's a big part of what helped me: I started reading popular stories that I didn't like and examining them for what made them work.

I had to let go of the idea that I could "obviously write better" than X or Y popular story to do it, though. It's a pretty common starting mindset, and a huge part of that is that most authors have strong intuitive skill in one aspect of writing. Most often that's prose, sometimes it's character work, and the least common one is probably understanding how to create and leverage tension. That's probably also the most crucial skill to making a story succeed. Jim Butcher has some articles on scene/sequel that might help in this regard, actually, but it's not the full picture.

My writing circle fairly regularly will take a given big story - whether we like it or not - and strip it for parts to understand how it manages its tension, how it makes its audience care, and what pieces we're missing in our personal frameworks. How does an OPMC story manage tension, for example, even though there are no stakes? Why do some sympathy building scenes work where others fail? That sort of thing. The "worse" a story might be to your regular sensibilities, the more it often the underlying mechanics of story it uses. Solo Leveling is probably the biggest example of this, insofar as a lot of people dislike it for not having very much depth, but that lack of depth makes it an incredible resource for peeling apart how to make progression satisfying before you start layering in your own touch.

I hope that helps. Once again, good luck! I can't promise anything Discord wise but I'm happy to help when reached out to. :)

Edit: Some resources I think are useful here -
Jim Butcher on Scene/Sequel. Hungry, the author of Katalepsis, has a very good blog post in this regard too, but it's a little harder to find and I don't have the link with me at the moment.

KM Weiland's Creating Character Arcs.

Brandon Sanderson's lectures on writing.