The Nefarious Plot
The simplest form of a plot is a “high-points plot.”
Take Romeo and Juliet. The high-points plot could be relatively detailed, or it could fit in the back of a postcard, in which case it would go something like this: Romeo falls in love with Juliet. Parents enemies. Lightning-fast romance. Secret marriage. Forced separation. Juliet pushed to marry Paris. Confusion. Double suicide. Parents chastened.
If you are the more detailed type of high-point plotter, you could have in stuff like the duel with Tybald, or the friar’s plot to fake Juliet’s death.
A more detailed form of plot is a chapter plot. My chapters tend to coincide with scenes, so it would go something like this:
1- A duel between Capulets and Montagues on the street. Supporting characters introduced, including Benvolio. Duel is broken up by the prince.
2- Montague interrogates Benvolio about the cause of the quarrel. Conversation turns to Romeo, whose behavior has been worrying his parents.
3- Benvolio interrogates Romeo on the cause of his changed behavior, and finds that he’s in love with Rosaline.
If you have no idea on how a plot should go, there are many guides to use, including Campbell’s the Hero’s Journey or (depending on the size of your endeavor) the simple injunction that your character should start the story in some sort of trouble and that his efforts to dig himself out of trouble should bury him deeper and deeper, until a grand climatic battle, confrontation, or effort is necessary to restore him to his normal life. (Or get him better off than he was when the plot started.)
Most people do know how they want the story to go, though. Depending on what you’re writing you probably know at least how it ends, and you can reverse engineer it every step of the way to see which scenes must be in there to make it work.
You should be aware that many beginning writers complain that once they have outlined the plot, they no longer wish to write the story. In that case, you might wish to consider simply doing a high-points plot and leaving your subconscious to fill in the details as you write.
You should also be aware that sometimes the plot changes as you write and characters take on a life of their own. This happens to some writers all the time, to others not at all, and to some occasionally. If it happens to you, you’re normal. Just roll with it, and change your plot as you go. Of course, then you might find yourself becoming a pantser.