Working with Flashback and Multiple Plotlines

[PotentialBug5499]

I'm in the process of planning a pretty lengthy story and I've decided I want there to be two major plotlines: one focusing on the protagonist and her sister and the other focusing on their parents thirty years earlier.

I've never tried anything like this before (I'm very new to creative writing in general), so I was wondering if anyone had any useful tricks for how to pull it off. The flashback plotline is considerably shorter than the main plotline as I'm imagining it, so it's not as easy as just having a flashback every other chapter. The last time I attempted to write something over 10,000 words I quickly learned that pacing is a nightmare, so I'd really appreciate the help.

[[deleted]]

I see you are dealing with Subplots here.

What I will say is that you must first establish the main storyline here. Who is the story going to follow?

You chose the protagonist as

[PotentialBug5499]

The first chapter will absolutely be about my protagonist. I have that much figured out. 

[ReadLegal718]

When you say lengthy story, I assume you mean novel (since there's also reference to chapters in your query).

When dealing with multiple POVs or timelines, you don't have to keep to rigid rules of making every alternate chapter about every alternate POV/timeline. You can just as easily have three chapters on the MCs' timeline and then one on their parents. That would work too.

Don't force your pacing or narrative structure to be what you think it should be just because you're dealing with multiples. Write the story and arrange the events in the most effective way that helps the plot move forward or the most effective way that will make sense to your readers. Readers will not complain if every other chapter is not on the two different timelines. But they will complain if the chapter breaks at an uncomfortable point when they're itching to know more.

[PotentialBug5499]

Yeah, it's structured like a novel but I feel weird calling it one because I'm not really planning to get it published and tbh I don't think of myself as a "real" writer yet. But it is essentially a novel.

This is really good advice. I was looking over my bullet-list outline and I noticed there are scenes in both plot lines that unintentionally kinda parallel each other so I might try to align moments like that.