How does staging affect the plot of Much Ado About Nothing?Give specific examples.

The most appropriate way to answer this question would be
to take a particular staging of the play and consider how that production's staging
affects the plot.  However, it is possible to consider some moments in the play in which
staging might affect what we understand as the plot simply from reading the play.  The
moments that occur to me most readily are the two moments in which Don John tries to
convince Claudio that Hero is unfaithful.

The first is in
Act II, scene i.  There is a masked dance underway, and different couples are
conversing.  Much about this scene must be decided by the company producing the play: 
Are men and women wearing masks or only the men?  What sort of dance are they doing? 
How is the dance performed; are all dancers onstage together?  It is just this sort of
scene in a Shakespeare play that reminds the reader that the play can't really be
understood completely unless it is seen live, as it was intended.  In this scene, Hero
and Don Pedro are dancing together, as Don Pedro has promised Claudio that he will
disguise himself as Claudio to win Hero's hand in
marriage.

As the dancers dance themselves off-stage, the
non-dancers -- Claudio, and Don John and one of his henchmen -- are left onstage.  We do
not know, simply from reading, how Don Pedro and Hero have acted together and if Hero is
flirting with a man she believes is Claudio or not, but Don John convinces Claudio that
Don Pedro has wooed Hero for himself.  The plot is concerned here because it could be
staged either way.  Hero could be presented as somewhat of a flirty girl who is
enamoured of Don Pedro or not.  And this would affect the plot because it would either
give Claudio cause to be jealous or not.  The question, for the time being, is cleared
up when, later in the scene, Don Pedro presents Hero to Claudio as his fiancee.  Don
Pedro has indeed wooed in Claudio's name as promised.

The
other scene that concerns Hero's fidelity is the scene written by Shakespeare to happen
offstage, the wooing of Margaret by Borachio in the name of Hero.  It would come at the
end of Act III, scene ii.  This scene is sometimes presented in dumb-show even though
Shakespeare did not include it in his play.  Showing the audience what it is that
Claudio sees can definitely change the plot for the audience since they can either agree
or disagree, based on what they see, about whether Claudio is justified in accusing Hero
of infidelity or not.

Both of these moments in which
Claudio is led to believe that Hero is not faithful to him could alter the perception of
the plot of the play based upon how they are staged.

The
essay in the link I've provided below on appearance versus reality in the play gives
some more suggestions as to moments where staging affects plot.