Ten things to think about to test the strength of your plot:
Develop a clear conflict in the action of your story. Identify the forces of opposition.
Your protagonist is an emotional being. Know where your character stands emotionally at the start of the story so that s/he can be challenged emotionally early on. This helps in developing the character's arc.
Know what your protagonist wants, why s/he wants it, and what s/he needs. The more specific the character's want, the stronger the plot potential.
Examine the emotional consequences to the conflict your characters face. Determine which ones define your theme and engage the audience's emotions.
Remember: Conflict doesn't come exclusively from the antagonist. Use other obstacles and complications to reveal character.
In dealing with the various problems (the conflicts), the hero must experience setbacks as well as successes to create tension. You define character as much through failure as through success. How the hero copes with these outcomes gives insight and meaning to character and story.
Characters are defined by the choices they make. Every story is really a series of increasingly difficult and dangerous choices that simultaneously carry your plot and illustrate your character.
Plots need to be based on action and reactions, cause and effect, to lead the audience from point to point. Use cause and effect plotting to make sure each scene leads believably to the next.
Conflict must escalate. All your characters have wants and needs, differing agendas, and these raise the level of conflict as your story progresses.
Audiences need surprise. The best surprises are the reversal and the reveal. Both must be plotted for. Reversals work best when the audience has been set up for one result and get the opposite. Reveals work best when the revelation has been cleverly foreshadowed early, but not given away.