One of the most useful dicta (I won't say "rules" because there are no rules) I came across early in teaching myself to write was "start as near the end as possible". It was a propos short fiction, and of course it's not really as simple as that, but there's a lot to be said for remembering it in novel-writing too. Later I came across the thriller-writers' dictum "Get in late and get out early", which is the same idea and equally sort-of-true (see here for a discussion of the "getting out" bit). And I usually find that students' MS have much more explaining of backstory and past history than they need, and it's quite rare to have too little. As so often, you needed to think all that out to write it, but we don't need to read it
But where does that leave you with the bits of What Happened Before which we really do need? The crucial underpinnings of feeling and thinking on which the events of Now are built: the lost relationship with the sister which has brought your MC back to their childhood home; the bullying at school which destroyed his confidence and so is wrecking his marriage; the difficult, lovable, hated parent who's now dying slowly in your spare bedroom. How do you convey that stuff?
If you have an external narrator - a knowledgeable entity, a storyteller, with privileged access to any amount of information and any number of heads - there's nothing to stop you simply narrating the necessary knowledge. That might be the best way for plain, fact-y facts, of course. As I was exploring here, sometimes Telling/Informing is the best way. But what if important past events need Showing/Evoking? What if you need bits of the past to have full emotional punch? We're talking flashbacks, aren't we.
The usual way to insert a chunk of Before is simply to write the bloomin' thing, slipping from simple past to past perfect until the reader's established in Before, and then making all our lives easier by switching to simple past for the rest of the passage:
Jane looked at the estate agent's details. The house was bright and new, with plastic windows and a York stone drive. It used to be so scruffy, all weedy gravel and paint peeling off the walls. Her father had raged about the chaos almost every day, but he had never done anything; it was as if he had used up all his energy in anger. And then one day he grabbed a palette knife from Mum and attacked the bit by the back door, hacking and hacking until there was a great hole, and shouting all the time. Jane started to cry, and then Mum scooped her up and carried her out of the house and down the drive ... It was all a long time ago, of course. Now, the house cost far too much. Jane dropped the details into the bin.
Note "It used to be so scruffy,", which leads the reader into the Before, and "It was all a long time ago", which brings the reader back to Now. And note how the narrative takes advantage of free indirect style to let the voice takes on a shade of child-Jane, in the Before sections. Of course experienced readers can cope without these leads if you make the break between Now to Before clear: a double-line space and a block of simple-past narrative of Before can do the job perfectly well. Then there's the present-past option (which I explored in more detail here), which is essentially the same with all the tenses up-graded by one.
Jane looks at the estate agent's details. The house is bright and new, with plastic windows and a York stone drive. It used to be so scruffy, all weedy gravel and paint peeling off the walls. Her father raged about the chaos, but he never did anything; it was as if he used up all his energy in anger. And then one day he grabbed a palette knife from Mum...It is all a long time ago, of course. Now, the house costs far too much. Jane drops the details into the bin.
But of course it's true that we don't remember in tidy blocks, we only remember the things which were significant. That needn't matter: a narrative isn't the same as a person remembering or even experiencing. Flashback is a narrative technique, not a reproduction of how people actually think, and that's fine. You just need to make sure that you teach your readers from the beginning that this is how the book works and this is how to read it. Make sure the first few jumps are particularly clear - give the reader enough hand-holds, as my editor says, and help it along with changes in the voice - and then you can trust they'll come with you.
But the point about how people remember does lead us into more interesting territory. Your character Now has a relationship with that past so we could stay aware of Jane Now, even as we're also admitted to her Before. Think about how you might write a memoir in first person. Would you write it like a straightforward novel, evoking the experience of this child who happens to share your name? Or would you keep you-as-adult present? Would you explain or comment on the child's experience? Would you fill in things the child can't know? How do you connect you Then to you Now? Now transmute that understanding into using Jane's Now to channel Jane's Before, and keep an eye out for words like "now" and "one day", which act as hand-holds:
Jane looks at the estate agent's details. The house is bright and new, with plastic windows and a York stone drive. Surely it used not to be like that? Yes, it used to be scruffy. As a teenager she saw it suddenly through the eyes of friends she brought home: all weedy gravel and paint peeling off the walls. But when she was small, she didn't notice. It was just home, the way things are to children. She heard her father rage about the chaos almost every day, but she didn't really understand it, and he never did anything; now, Jane wonders if he used up all his energy in anger. And then one day he grabbed a palette knife from Mum and attacked the bit by the back door, hacking and hacking until there was a great hole, and shouting all the time. Jane started to cry and then Mum scooped her up and carried her out of the house. The drive seemed very long that day, even though it was only actually thirty yards or so; a maple leaf came swirling down and landed on her tummy where she was bent in the middle in Mum's arms. But she can't remember how old she was, although she must have been heavy: too old to be carried except in an emergency. Her feet can still feel the sting of gravel under bare feet as her mother finally put her down. What was her mother thinking? Was she afraid for them? There is no knowing, now. And it is all a long time ago, of course. Now, the house costs far too much. Jane drops the details into the bin.
You'll notice that despite my reservations about solidly present-tense narrative, Now is present tense here, because it's a real help in keeping the reader with you as the narrative slips to and fro in time (as I did so much in A Secret Alchemy here, for example). Of course it would be perfectly possible to do this as simple-past and perfect past, but even this post is going to have to stop somewhere so I'll spare you the demo.
There are real riches to be had, in handling Before in this sort of way, narrating the slipping to and fro, rather than making a jump-cut and crash-landing in Before. It's much more fluent, for one thing. Instead of having to grab your reader by the hand so that you can move into the flashback - or jumping without a hand so that you're relying on the reader to hang onto your coattails - you have the reader by the hand all the time. Jane's thinking Now can connect apparently unconnected bits of Before, rather than them being chopped-up scraps on their own. That's not just about fluent storytelling, either. Jane is acting as the narrator (or perceiver might be a better word) of her own past, connecting bits of Now to bits of Then as we all do to make up a single human life. This is what I was getting at, in 17 Questions to Ask Your Novel, with "Where does your narrator stand... relative to the events of the novel?".
What's more, the more conscious we are of Jane Now as the perceiver of Before, the more we're aware that she may be inadequate or unreliable as a lens on the past. That paradoxically widens our sense of the world of that past: we might see things beyond Jane's perceptions. And since it's Before which is powering Now, keeping the two in relationship makes the drive within Now much more powerful. In Past and Present Tense I was arguing that in many ways past tense has more drive (contrary to so much that the stupider CW pundits say), because it keeps up the pressure of the past behind the present. I'd suggest that it's true of the temporal structure of your novel, too. Try it on a story, if you don't want to risk it in the WIP till you're more confident. Some of my most successful stories started as exercises: yours might too.
PS If you came to this post via Twitter and a link from my @itchofwriting persona, you might want to know that I'm not tweeting from there any more, but consolidating it with @emma_darwin. So if you'd like to keep up with what's going on here, do follow @emma_darwin, and you can be sure you'll hear as soon as a new post goes up, and of course any other news, trivia or argument about writing that's occurred to me...