1.    Being Quiet.  Do not talk, whisper, sing along, unwrap candy, chew gum, beat your feet in time to the music, or make any noise disturbing to audience and performers.  And though not quite in the category of noise-making, vigorous fanning with the concert program can be distracting and, now that air conditioning is everywhere, quite unnecessary.

2.    Being Punctual.  Be on time, which means arriving well before (at least five minutes) the music begins. If unavoidably late, wait until there is a break in the music before taking your seat.  Conversely, do not leave until the concert is over and the last echo of applause has died away.  If you must leave early, try to do so at intermission, or at least wait until the selection being played has been completed.  Getting up and walking out, especially when a piece is in progress, is disturbing to the rest of the audience and - let's face it - insulting to the performers.  If convinced beforehand that the concert will not be to your taste, it would probably be best to find another source of entertainment.

3.    Knowing When to Applaud.  First, let it be acknowledged that performers always appreciate applause.  However, audiences sometimes applaud at times when it is not appropriate.  In general, when listening to a symphony, concerto, suite, sonata, string quartet, song cycle, or any piece consisting of several closely related sections or movements, withhold applause until the entire work has been played.  Occasionally, applause may occur following the first movement of a concerto, which - with its dramatic intensity and brilliant cadenza - will often be the high point of the entire concerto.  Look for a signal from the conductor here.  With a simple hand gesture, the conductor can indicate clearly enough that it is not yet the time to applaud.
    In short, the Forgoing simply means practicing good manners.  Other audience members and certainly the performers will be appreciative, and your own enjoyment will be enhanced.  Great music, beautifully performed deserves complete, quiet attention.  It's the only way to listen.