I thought one of the primary steps in writing was knowing which moments you were going to build to.
This comment stuck with me because it's very much how I approach writing. I don't start writing when I first get an idea. I let the idea simmer in my brain and become a story (an idea is not the same as a story, but that's a topic for a later entry). I think about who the characters are and what makes them tick and what happens to them and how it's all going to end. In one case, I even knew what the very last line of the book would be before I started writing.
I don't outline, but I do have the general story arc in my head. I know how it starts, and I know how it ends. And in between the start and the end I have an idea of the milestones along the way.
The milestones are often major events in the plot. Or they can be moments when nothing much seems to happen but a character has a turning point that changes the course of his arc over the rest of the book.
But just as important as those big moments is how we get to them. In between those moments, a lot of work has to be done. The characters have to get from milestone to milestone in a believable way - and that's not just the plot but the characters' emotions and psychology. Character X can't start behaving in a way that totally contradicts everything that's been established about him just so he can make the plot go the way the writer wants it to. (I see this in books, and movies too, and call it the Character Arc Loop-De-Loop). Likewise, the book's pace and setting need to build to the moments. With some exceptions - such as a fight-for-survival thriller that takes place over one night - the book needs to breathe. It needs to give the readers an anchor, a stake in the story and the characters' fates.
A character's big life-changing event will have more impact if the reader understands about the character's life before the big event. This will make the event resonate more. What's been lost? What's been gained? Where does the character go from here? And why should anyone care?
The big moments should grab you - the builds in between the moments help ensure that the big moments do grab you.