One of the biggest pieces of advice regarding writing that I've heard from...well...nearly everyone, is that you need to hook your readers early, preferably on the first page. I was in a discussion on another website, and I got to thinking, What the hell does that really mean?
Too many writers, in my humble opinion, read this to mean they have to begin with some sort of gangbusters action. Start with a battle! A car chase! A murder! I, on the other hand, think this is often a horrible way to start a novel. Sometimes starting off with action makes sense because it fits the overall pace of the story, but I usually wonder why I should give a shit about this football game/rape scene/courtroom drama. I have no idea who the characters are, yet I'm supposed to be instantly drawn into caring about the outcome? I don't even know who to root for yet. What if I accidentally start pulling for the guy who eventually becomes the villain?
However, mature writers know that there's more to hooking people than just a truck explosion or torrid love scene. You can hook a reader with the right catchphrase or dialogue. Maybe you've found a unique way to describe a setting, and the mood overtakes the reader from the outset. Whatever it is, it's more dependent on your talent as a writer than it is on whether enough gunshots are fired.
That said, whatever way you start your novel, you have to be able to grab a reader's attention early. Especially in today's culture of instant gratification, people get bored quickly. There are so many other outlets for the mind that getting someone to take the time to read what you wrote requires effort. Most people will give a writer the first ten pages or the first chapter to grab their attention. If the author hasn't captured that person's interest by that point, most readers will simply put the book down and look for something else(even "serious" readers will do this). Some are even more harsh, looking at what comes out of the first page to see if they need to continue. While I find this confining, it's still the reality of the world in which we live.
This is where beta-readers are so important. A good beta-reader will be able to tell you if you got his or her attention. If you didn't, ask why not. Ask what you could've done to grab someone by the balls and not let go. Sometimes the answer is nothing. Maybe you have a bad idea, or maybe you have a good idea that doesn't translate well to books. Whatever it may be, if readers don't read you, your work will be wasted, so move on. However, there's usually something that can be done to spice it up, and our beta-readers, being as self-important as we writers are, will leap at the chance to tell you what you could've done to get their interest.
Remember, find a way to hook 'em. Remember as well that such a thing can be more than a massive battle. Just do something different and in a way that gets notice. If you can pull people through that door, they'll find themselves walking willingly, even eagerly, before they know what hit them.