So for that past two weeks, I've been working on the blurb for my fantasy novella. In all seriousness, I think it's harder than writing the book itself. Having to whittle down the plot and four POV characters to just 150 words is a nightmare, but boy is it a great exercise. I've learned more about my characters and the plot of the story than I have done while outlining and writing three drafts. The blurb process forces so much clarity of character and story that I realized that it's the first thing I should write before attempting the first draft.
A big help structuring the outline came via Libbie Hawker's book "Gotta Read It: Five Simple Steps to a Fiction Pitch that Sells." In her book, Hawker describes how a blurb should be structured using five simple, yet important, questions about your novel: 1. Who is your main character? 2. What does she want? 3. What stands in her way? 4. What will she do, or what must she do, to achieve her goal?5. What is at stake if she fails?
What I did was answer these five questions for each character and then I wrote a paragraph for each laying out the structure above. With four POV characters, obviously using four such paragraphs would be way too long, not to mention there would be no room to mention the plot. But it gave me a clarity of each character's predicament and how they relate to the plot for me to go ahead and take a stab at the blurb itself. I ended up with one that was 365 words in length. Way too long for a blurb, which really should be no longer than 100-150 words.
It was in the cutting down from 365 to 150 that I found the holes in my book's plot as well as what was missing from my character's arcs. A negative consequence was that when all was said and done, my 150-word blurb resembled the plot of A Song of Ice and Fire. This happened because I chose to focus on the plot instead of the characters and their stories. So back to the drawing board I go. Oh, and a word to the wise. These blurbs are perhaps the most important part of marketing your book. In addition to a nice cover, the blurb is what's going to sell the book, so you should take lots of time, do many revisions, and get lots of feedback before deciding it is complete.