What Makes a Good Blurb?
Strange but true: it's entirely possible for an author to write a fantastic book, but when it comes to the blurb, something goes very wrong and they can't quite make it pop like it should. Is this a defect? A quirk of the art? No, something far more simple - creative writing and copy writing are two different skills, and it's entirely possible to have one but not the other. Nowhere is this more evident than among the independent authors who self-publish today.
The Problem with Blurbs
I've talked before about how to spike a book (which is to do something wrong in the marketing, such that the sales tank) and what I said about blurbs was this: it needs to be enticing, representative, and include some key pieces of information.
Blurbs are no different from any other form of advertising copy. Their most basic function, like the cover, is to make people want to buy the book. That aim should be the one and only thing in mind when writing them. The majors obviously have copywriters who handle this kind of thing, but indies need to go it alone, and that means knowing the basics of how to make it work.
It has to be enticing enough to draw the reader in. It needs to suggest just enough of the plot to get them interested, but leave out enough so that the major questions asked are not answered. It needs to show what's at stake in the story, but not how the stakes play out or how it's resolved.
So yeah, no spoilers, obviously. It's a fine judgement between too much and not enough, but the rule of thumb that I like to use is that the resolution of the apex of the book - the most important question, the final showdown, the highest thing at stake - cannot be revealed, but one other important thing in the plot can be. The death of a character, the discovery of an important piece of information; as long as it's not the big one, it's fair game to hook a reader's attention.
The Influence of Tone
When I say it has to be representative, I mean that the tone has to be suggestive of the book. A serious high fantasy book uses different language in comparison to a chicklit romance, and that language should have a particular tone. Whether a reader knows it or not, they will be influenced by the tone - whether it sounds dark, or happy, or urgent, for example - and the correct tone is the one that appeals the most to the book's target audience.
What The Reader Needs to Know
It's absolutely staggering that many indie book blurbs seem to forget to tell the reader key pieces of information, like, say, the name of the main character, in the interests of seeming enticing or mysterious. This does not work. It's a noble goal, but sacrificing clarity doesn't encourage people to read on to find out. Here's the general idea for what info to include: does it happen or appear in the first few chapters? Then yes, that info can and should be there. If the main character's name appears on the first page, for example, why wouldn't that name appear in the blurb? If the villain's name is known by the third chapter, why wouldn't that appear as well? If, however, the evil-doer's motives are not known until the last third of the book, then that info should be withheld.
Why is this, you might ask? Simple, really. Something that is revealed in the first chapter presumably has no build-up or importance attached to the reveal. In fact, it's likely told early because the reader needs to know it to get the rest of the story. Something that's revealed much later on presumably has a lot of build-up and importance attached to it, and it's not essential to know it immediately. That's the dividing line for information in the blurb.
A quick note on this: blurbs are often far too short. This really isn't ideal for an ebook, for example, if Amazon allows a nice, usable chunk of text. A blurb of about 300-400 words, nicely formatted into paragraphs, is much better than the two or three lines that appear on the back of a physical book. Again, refer to the bestseller lists and look at how they do it.
Blurbs are important because they are a part of the presentation of a book. Sometimes, they will be the first thing a reader encounters, and if they can't pull them in, the sale will be lost.