It's important to realise that flashback isn't the same in all its forms. It's not just one thing. It's six main types. Some of the six require a complex structure of their own, quite different from the conventional three act linear structure, a massive scaffolding (these are the double narrative types, where you jump back and forth). Others, like 'where were you on Tuesday night' (a type I call 'flashback as illustration) are not structural, they're just, as I say, dramatised backstory that won't affect your linear three act structure. Your job there is just to be consistent.
My answer to Melisha
Oh thanks, Melisha. I hope it's useful for you. If you don't mind me suggesting this, be sure to read the material in the book on conventional narrative first, because you need to get your head around my take on the three act structure since the way good flashback structures work is that you jump on precise points in stories that are actually three act structures in themselves, A lot of people reading my books just jump straight to the flashback chapters and then get in a mess. Unfortunately, you need to hasten slowly with this stuff.
The reason is that there are many kinds of flashback and many odd things about it. It requires a different mindset from conventional narrative. For example, in certain complex forms of flashback, the ones where you have an ongoing story in the past and an ongoing story in the present, a character can be a protagonist in one time frame (that is, seen from the inside) but an antagonist in another time frame (that is, seen from the outside by another person who is the protagonist in that time frame). It's a bit of head spinner at first, but it's to do with the fact that good flashback structures turn your film into a detective story and that requires you to create characters who are mysterious because seen from the outside in one of the time frames. So don't think of flashback just as a way to stick in a slab of backstory. Think ' a detective story about human motives'. My motto for complex flashback is 'the story in the present is a mystery story and each flashback is another clue'. That energises it. Otherwise you're just doing windshield wipers, back and forth, back and forth.