The hook is the single most important element. No matter how captivatingly brilliant your work may be, no one will read it if you fail to snag potential readers at first blush. It should be one of the first -- if not the first -- things the reader sees. Thus, you'd better make it a great one.
A well-written hook does more than demand attention. It reaches out and shakes the reader by the collar of his shirt. It's probably also the hardest element on which to offer advice. It helps to have a firm understanding of your work and other books in your genre when writing a compelling hook. Ultimately, your hook needs to pique the reader's interest.
As an aside, you may get those fifteen seconds if your hook was effective. You won't get anywhere near that if it's not.
You must clearly identify your book's genre, theme, and salient plot points. Give your readers a taste of what to expect, but don't give it all away. There's something to be said about about suspense, and Alfred Hitchcock said it best: "There is no terror in the bang, only in the anticipation of it."
Don't be so quick to pull that trigger. Your readers will want to do that all on their own. You'd be doing them a disservice if you didn't let them.
On the other hand, a blurb is expected to be open-ended. But, like your opening, make sure you leave a hook at the tail end. Why two hooks? Any angler will tell you there's a reason why fishing jigs often come with more than one hook -- you've a better chance of catching fish that way.
Marco’s life as a messenger isn’t great, but the work is easy and he gets retirement pay in thirty years. Little does he know his life teeters on the cusp of change.
When an unusual assignment sends him overseas, he finds himself stranded in foreign lands. With no way home and no hope of making his delivery, he sees sour prospects for attaining his modest retirement dreams, much less getting out of the whole mess alive. Even that wouldn’t be so bad if he weren’t constantly outrunning pirates, embroiled in international intrigue, and attacked by a hummingbird with an appetite for human brains – that’s just the start of his misadventures.
But lurking in the wings is a much greater threat than getting sacked from his job. The fate of an entire civilization may well rest upon his scrawny shoulders. In spite of himself and quite by accident, Marco may yet become the hero he strives not to be.
On an unrelated note, that part about juggling dangerous gas-powered tools was a figure of speech, so please don't attempt to juggle chainsaws.
Have fun (and be safe) writing!