One thing that happens after you sell/publish a book is that people ask you to read their manuscripts. Sometimes fellow writers are seeking feedback or constructive criticism; other times they're looking for blurbs to help them in their effort to sell their book. Sometimes, other published authors come a callin' to ask for blurbs for their front or inside covers (as I recently approached a number of successful and I guess I'd say, even more successful, authors).
The rate at which I've been asked to read manuscripts has increased a little lately, and it's got me thinking about how to approach this task with the attention, openness and humility it deserves.
First, there's critique. What sorts of feedback are really useful to a budding writer (or experienced auteur)? What kind of comments will keep them going rather than shut them down? At what point does attention to detail become nitpickiness? At what point in a work should you even ask for feedback? Is it better to offer your impressions in broad strokes, or line-edit/comment the manuscript? What do you think?
I have found that the approach that works best for me as a reader is to identify the manuscript's strengths and its weaknesses, and then look for concrete examples of these patterns to show the author. Although I may not find a manuscript to be a scintillating read -- either because it's not my preferred genre, or because the writing just isn't my cup of tea -- I can generally find several examples of good writing or technique, and I don't hesitate to share them with the writer. I think identifying patterns or tendencies is important, because it takes a long time to spot them in your own writing (good or bad).
It's quite humbling for someone to place their work in your hands. It's a brave act. I still have a terrible problem letting people read my work early on, and I believe my work has sometimes suffered for it (i.e., I have, on occasion, turned in what amounted to first drafts to my editor instead of polished manuscripts, thereby embarrassing myself). I'd like to help other writers be less precious about their work and learn to depersonalize critique to the extent that they can, in part because I think it will help me on my mission to do the same.
Finally...I would suggest that you take any critic's feedback with a grain of salt. It is highly subjective stuff, after all. It's almost impossible to consummate a work of fiction without some deeply felt convictions about character, plot or premise. Cling to those convictions even as you hear others' critiques of your work, because you'll need to return to them time and time again to remind yourself why you entered this mad escapade in the first place; the purity of the original idea motivates as no other factor can.