need help on the structuring of gcse aqa english lit essays!

Hey there! I'm Holly, an offer holder for RHUL's English & Creative Writing degree. In my GCSEs I managed to get 9s for both English papers, so though it's been a little while since I studied, hopefully I can help you out a bit.
First off, when it comes to 'Big Ideas', it's really important to remember that these are themes, NOT events. Structuring your essay in a chronological order isn't important most of the time - but it can be helpful when talking about the Ideas themselves. (I know this sounds odd, but bare with me here.)
For example, let's say we're doing this essay question: Starting with this speech, explore how far Shakespeare presents Macbeth as a violent character.
Your 'Big Ideas' might be Heroic Violence (Macbeth's punishing of traitors), Murderous Violence (killings committed by Macbeth himself) and The Violence of Others (how Macbeth's actions compare to those of others in the play, who are arguably equally - or more - violent). Personally, I'd argue in all of these themes that though Shakespeare presents Macbeth as a violent character, the violent behaviour he exhibits is somewhat normalised within his society. Heroic violence (e.g. the punishing of rebels and traitors) is seen as honourable, and we seem him being rewarded for it at the top of the play. Similarly, though Macbeth commits murder, he's actively encouraged to do so by others (e.g. Lady Macbeth), thus remoing some of the taboo of this act. Finally, the violent behaviour of others - such as the language used by Lady Macbeth, the killing of Macbeth by Macduff, and the like - create a culture of violence which Macbeth himself perpetuates rather than initiating.
As you can see from the example above, I'm not overly concerned with chronology in this response - so why have you been given advice that seems to contradict what I've suggested? Well, that comes down to the nature of the question presented. I find it easiest to answer these questions by categorising them first, because that helps me identify the best way to tackle them. I'd suggest the following categories, based on the questions from previous years:
I've broken down the previous questions by theme in the image below for you to illustrate my point:

So why does this matter? Well, we can establish a pretty simple rule of thumb for how we tackle questions - anything Comparative, Dynamic or Thematic usually doesn't need to be handled chronologically, but a Transformative question should always be handled in this way. (There are obviously exceptions to this rule - if the question asks, for example, how Lady Macbeth & Macbeth's relationship changes throughout the play, then this would be both Dynamic & Transformative. The key here is to recognise when you're being asked something Transformative - if there's any indication this is the case, then you should be looking at things chronologically.)
Now, the main problem here is that the examiners actually don't care that much how you handle things, so long as you hit the right general points. For a Transformative question, you can still work in your 'Big Idea' structure if you talk about chronology/progression throughout the play within these paragraphs. The main thing is that you do talk about any notable changes in some way. (Typically examiners reward working chronologically within Big Ideas more than they do working chronologically overall, but this is more of a technical point & you don't need to stress about it too much.)
TLDR: If there's any reference to how something or someone changes, develops or transforms in the play, always write chronologically. If the question asks anything else, you can work by your 'Big Ideas'.
Hopefully this helps! If you need any more clarification, just let me know & I'll be happy to explain things in a different way!