You may or may not have heard the term inciting incident. In screenplay terms, it's known as the catalyst. Basically, it's the THING THAT HAPPENS that creates CHANGE and STARTS THE STORY.
Notice I said CHANGE and not ACTION or CONFLICT. Of course you want conflict from the get-go; it's what creates tension and intrigue in your opening pages. But it's the incident that creates CHANGE for the main character that drop-kicks your plot forward. And it's important to time it well. As in, no later than the end of the second chapter (which seems to work well for me).
Some familiar examples:
The Chronicles of Narnia by Lewis: Lucy discovers that the wardrobe actually leads to Narnia.
Harry Potter and the Sorceror's Stone by Rowling: Hagrid tells Harry he's a wizard and says he's come to take him to Hogwarts.
Hunger Games by Collins: Katniss takes her sister's place as the District 12 tribute.
Admittedly, it's easier to pick out these Moments of Great Change in novels that have already been written. But it's important for you, as a writer, to identify the PRECISE MOMENT when something in your main character's life changes dramatically, thus setting the rest of the story in motion. The event is life-changing in some aspect, and without the event, the story wouldn't happen. So it's important to know exactly what this incident is, and how it leads to the unfolding of everything that happens afterward.
Examples of inciting incidents:
- Someone dies
- Something is won -- or lost
- Something is discovered (not any old something -- a life-changing something)
- Something happens that is the exact opposite of what was expected
- Something is decided (by the main character) that changes the course of his life
Once you've got this incident nailed, it acts like a springboard. Sure, it's easy to get derailed or defocused even if you DO have an excellent inciting incident. But that's the beauty of this journey--we just keep learning and growing, one step at a time. So make sure your inciting incident is clear and well-placed. The rest of your novel depends upon it.