What I've done in the past:

I usually start by taking some time to quickly read the whole story. Keep in mind that "quick" means I might miss some minor details because I'll be flying. But it will give me an idea of major plot holes or issues that need to be addressed right out of the gate.

Then we'll spend most of our time by going chapter by chapter, addressing minor  holes (she's still standing but two paragraphs ago, she sat down), grammar issues, and dreaded monsters like "too much telling, not enough showing" and "these sentences all need to be tightened by half." 

My standard disclaimer is that art is subjective. I'll make 1000 suggestions, and I'll explain the reasoning behind them, but, in the end, it's YOUR story and YOUR voice and if you disagree with me, it's not going to hurt my feelings.

That said, this time will likely be different!

The mentoring session is much shorter this round than in the past. If you've got a larger work, there won't be time enough to get through the whole thing line by line. We can start at the beginning or tackle problem chapters you are concerned about.