A 'blurb' is a short, active synopsis of a story for the purpose of providing the reader with a general idea of the tone, scope, and plot/purpose of your work.
The major mistake authors make in creating blurbs:
1. Writing too much. I have seen 'blurbs' that covered the entire back of a book and that is simply saying too much!
2. Being too bland. It can be hard to write about your creation, so often authors distance themselves into bland, hesitant, awkward or stilted phrasing.
3. Being too vague and using specialized terms or nomenclature. People in your field or who share specific beliefs are familiar with the specialized terms, but someone else will not understand the 'in language'.
Tip for Writing a Blurb:
1. Take an index card. Old school but it is a visual, so bear with me.
2. In no more than about five sentences give the overview of the book. Pretend it is being listed in a viewing guide for a movie. This is the 60-second commercial for your book. This is the tease that will make people want to learn more and read your book.
3. Add active words to make the descriptions vivid and dramatic.