What is the difference between a critic, a Beta reader and a mentor? Think about that one. I'll give you some space and wait below...

A critic tells an author what they've done wrong (hopefully also right). A Beta reader tells the writer how they experienced their story as a reader. And a mentor...asks the author about the story. Oh, they read the story, but more importantly, they ask questions about it.  Sometimes strange questions about it, sometimes annoying, overly-pedantic questions about it and sometimes even gobsmackingly dumb questions about.

But they ask. They ask, ask and ask again. Questions are the mentor's greatest tool and greatest weapon. It's their strategy. That's what makes them so valuable. They ask about details, they make their author think about the story in new ways, not just feel and dream about it. They work into the corners where only the tiniest of toothbrushes can reach. They do details. 

Some writers are enthusiasts (see Types of Authors and How to Handle Them) and will gush non-stop about their work. But if you listen carefully, you will normally discover something fairly quickly. The author is FEELING about their story, not THINKING. They are seeing it play out in their minds as head cinema, but when you ask them pointed questions like, OK, why does Carla smoke while riding her motorcycle? or Why is the fact that Lance has a tattoo of a rattlesnake on his neck important to this scene?  they won't be able to tell you. They just FEEL that's right. 

And that's why they need you, their mentor. 

Because feelings are good. Feelings are great. Feelings create a lot of disjointed plots, flat characters, incoherent scenes, failed drafts and shitty, shitty novels. 

It's thinking and logical processing that's called for when the dreaming is over and the reality of getting good-quality stories on paper sets in. 

That's one of the first tasks of a mentor. Getting the author's head out of Dreamland and their fingers on the keyboard with a solid structure and plan for chapter one.