One of the very first bits of clear writerly advice I ever came across was the short-story writer's dictum of "Start as near the end as possible". Later, I encountered the thriller-writer's "Get in late and get out early", which is a double-ended version of the same idea.
Certainly it's rare for me to see a beginner's novel that starts "too late" in the story, whereas perhaps the majority either simply should start at what's currently chapter three, or the writer's realised that, and tacked a zingy prologue onto the beginning, in the (entirely folorn) hope that it will compensate for the next two chapters of background-filling and scene-setting. And in short-story terms, I've lost count of the stories where everything is devoted to that preliminary stuff, and the actual turning point, the moment of change, the point of the story, goes for nothing very much. As I said here, an epiphany is only an epiphany. It doesn't magically transform pages of first-draft writing-your-way-in, into a story worth telling.
Of course, sometimes, a story idea comes to you in the form of that start. If your ideas is: "If you were having a peaceful picnic with your beloved, and a runaway balloon sailed off with a child inside, and what you did next was part of what caused a death ...?", then clearly, the picnic-plus-balloon is a good place to start, and the rest of the novel is built from what that event did to the whole structure and texture of the character's life. (Ian McEwan's Enduring Love, since you ask).
But often your first idea isn't the opening. Maybe you know that the accident is the climactic crisis; or it's the searing midpoint to which the whole first half was rising, and after which everything is changed. (It can be an instructive exercise to take the big moment of any story, and imagine in that way what other story might have been built round it. See John Yorke's Into The Woods for everything you need to know about midpoints, crises and everything else). Or maybe you have a fully-imagined fictive person, or a real historical character, who has a whole life: which section of that continuum should you write? What's too late, and what's too early? I've blogged about endings, and some day I'll blog about epilogues, but the question of where you start is really a question about how do good openings work?
It's worth thinking very hard about the opening instability: the thing that will make us know, right from page one, that something has to happen. That's why the waking-up opening is something which needs to be interrogated fiercely, because chances are there are better places to start. It's also why having a body on page one is almost never a bad thing - and why so often crime series on TV start with the innocent walker's dog nosing around in the bracken. Don't go and put that kettle on just yet ...
Then there's the idea of the promise, which Andrew Stanton talks about: how the opening expresses to the reader/viewer the promise that this story will be worth their while. What is that does that? The blurb has told the reader why they should bother to buy the book: the job of the front page is really to answer the implicit, "Why should I bother reading on?" and, to be crude, on every page you need to answer, implicitly, "Because ... because ... because ..." That's even more true in an era of e-books and "Look Inside": browsing potential buyers have no choice about where they first dip, so the writer must assume it's Page One.
And you could think about storytelling as a structure of fortunately-unfortunately: if you start with one, how quickly will the other come along, for your characters to experience, and thereby be jumped out of the tracks of their lives up to now, and have to find and cope with a new path?
The judges of the Historical Novel Society's novel competition made a point about openers in historical fiction which is also more widely relevant: that readers are drawn in by otherness: "... at the outset we need to stress the things we do not share with our characters". Yes, we read stories partly to explore, re-experience, process our own sense of what it is to be human, but if that were all we wanted then we'd only read life-writing about people like ourselves. We read fiction, or life-writing about other people and places and times for its Otherness. So one part of the promise of those first few pages is to show how this story will give us that otherness.
Of course, you may have a character who's also a narrator: a character who experienced the events of the story, and now wants - no, needs, urgently - to tell you what happened, because ... . It might be Nick Carraway in The Great Gatsby, or the narrator in Dick Francis's Straight, which I examined here, or it might be Jane Seymour in Suzannah Dunn's The May Bride. Their own developing understanding of what happened to themselves* is as much part of the story as the deaths and adulteries among the others.
But you don't have to have a character narrating from inside the dramatis personae to work in this way. With an external narrator - a storyteller, if you like - you have in your hands the same, beautifully flexible way of controlling just how many sweets you let your storyteller drop, to lure us on: "The summer she was fifteen, Melanie discovered she was made of flesh and blood" (Angela Carter's The Magic Toyshop). Or "A young man, young but not very young, sits in an anteroom somewhere, some wing or other, in the Palace of Versailles". (Andrew Miller's Pure)
So both internal and external narrators can begin their story at the moment which the ending showed them was "where it all began". McEwan's narrator begins, "The beginning is simple to mark", but I know I've read novels which opened with the narrator, internal or external, actually debating "Where did it all begin? With X? Or Y? Or - no - really, it was Z". Which of course is really just the narrator dropping some sweets in a slightly more subtle way (or tiresomely rhetorical way, according to taste) than Dick Francis.
So what does this all mean for where, and how, you should start your novel? That debate is the clue: what, really, is the journey of the novel - the chain of important-causes-and-permanent-effects, the into-the-woods-and-back-again? Once you know that, then you know where to look for the moment which is the journey's beginning. And once you've understood the story-journey, then you can start to work out the plot-route, and this is where things like instability, promises, and bodies on page one come in: what makes us want to get into the car, and what starts the engine?
* That's also one reason that first-person-present-tense can be so limiting and inflexible a mode of telling a story: you have neither character-narrator's knowledge-after-the-event, nor an external narrator's wider capacity to tell us truths from beyond what an individual character could have known or thought in the moment.