As Joanna Penn so admirably summarised it, there has to be a sequence in the events of the plot, put in its simplest form as Acts 1, 2 and 3 - 25%, 50% and 25% of the book respectively.. In addition, Act 1 contains an "inciting incident" half way through and a plot point at the end of Act 1 where everything changes for the protagonist. Act 2 contains the second plot point at the midpoint of the story, "a moment of truth" which the protagonist has to process and Act 3 begins with the third plot point as well as containing the Climax of the whole book. Welland expands on this in her useful book "5 Secrets of Story Structure". Throughout the history of opera and theatre, this has been the basis of plot.
James Scott Bell goes one step further by suggesting starting with the middle of the book. For me that works very well as I tend to change my mind about the opening of the book in the search for maximum dramatic effect. He also gives examples of plot structure that pertain to the inner personal transformation process of a protagonist which my mindset likes. I tried using the snowflake method which sounded attractive but it didn´t work so well for me.
As an artist, I like to improvise on canvas. I don´t like to plan. My two published non fiction books did not have a plot as such. I therefore decided to write my first draft for the novel as it emerged and make the adjustments to structure afterwards. It all seemed so simple. I had the freedom to constantly open up to new ideas. However, the changes to plot structure were harder to implement this way. Whole chunks of writing had to be moved either backwards or forwards to tighten the structure. This wasn´t helped by my indecision about the use of flashback and points of view which I wanted to use to create tension around the conflicts. I had to attach "weight" to the significance of characters and events I was writing about. It became a clumsy time-consuming process. Nevertheless, I learnt a lot from the acrobatics of the process, much of it through osmosis!
Now that I´m pondering on my second novel, I´m sifting through the ideas and themes with "plot structure" firmly placed foremost in my mind. I have opted for Bell´s approach of starting with the middle of the novel and then returning to the three acts. A very different way of working for me but one which will avoid the problems I had with my first fiction book. It feels more comfortable for the long term. Once the plan is written up, I will start writing my first draft. So wish me luck!
The books I recommend reading are the above. I am in no way affiliated with the authors or publishers.