Oh for inspiration and the time and ability to just sit down and write...
I love it when a story is just "there" and all I need to do it is move my fingers and it writes itself. How fun!
That kind of writing usually begins with a killer first line. And while your first line doesn't have to be the best one ever written, it needs to have a wow factor, a reason for the reader to keep reading. It should be interesting and intriguing. The second line should tempt you to read the third line and that leads tot he fourth...until you are knee deep in the mystery, the romance, the thrill, the scare, whatever, until you can't put the book down.
But there is a disadvantage to making the shock and thrill of the first couple sentences show off like fireworks. Don't you hate it when a read a book that starts with awesomeness, followed by a quieter 2nd line, and even milder 3rd line?
It all falls back to that fantastic, perfect first line. Which leads me to ask, "Why write an amazing firt line just for the sake of having that "wow" first line, if it's going to be followed by a disconnected first paragraph, which is the real beginning of the story?
I've heard is told you can't write the perfect first sentence until you've written the ending of the story.
Because it's not until you completed the story that the characters are all well-rounded and developed, you plot lines have all the wrinkles ironed out, and you know your story like the back of your hand. Once you are to that time, you can write a first line that not only intrigues, but also subtly foreshadows AND begins with something that fits with the story and is totally unique.
So if you are grappling with your first line and think you don't have it perfect, stop fretting and just write. After you've written the ten chapters, go back to that first line and think about how the story has progressed. If you changed it, would it make the beginning better? If not, keep writing.
Your first line is not written in stone. You can change it later.