The Nuts and Bolts of Editing
If you can first identify the macro issues going on in the book, then try to drill down to identify the mid-level issues that may be causing them.
- Tone of the book should stay fairly constant
- do the good guys resolve their struggles?
- do they make sense alongside the settings, or do they not fit with the setting?
- does the story need a new character in order to complete the connections and circuitry between existing characters?
When you communicate all this to the author, it helps smooth the path if you start the letter saying something good about the book. Think of your letter as a praise sandwich. Put praise at the top and at the end, and lay out all the issues you have found, in between. Praise is not just a formality. You want the author to take what the book is doing well and bring out more of it.