I found a website that gives us the exact "science" for writing blurbs. It includes some helpful Do's and Don'ts.

Do's:

Reference the genre and central theme

Create intrigue around the main conflict

Dive right in and introduce your protagonist

Keep it short and punchy

Reference your book-writing or professional status, if it relates to your book

Don'ts:

Give away any spoilers, no matter how tempted you are

Give a summary of the first chapter

Open with "In a world," or any other overused phrase

Give everything away

Say how amazing your book is

Compare yourself to other writers or your book to other books

If you like to see some blurb examples from famous books check out the next part.