If you don't want to look like a philistine when you attend the theatre I have put together a little list of things you should and should not do while attending the theatre (or any live performance for that matter). 

DOS:

• Do arrive at the theater with time to spare.  Check your curtain time.  Some shows are starting at 7:00PM on certain nights to get folks home earlier, particularly those with kids.
• Do turn off your cell phone and for the love of all that is holy, DO NOT text during a performance.  I can't believe I actually have to write that, you know who you are. Put away the cell phone and forget you own it for the few short hours.  You’ve shelled out your hard earned money to be transported elsewhere, why interrupt it with digital detritus.
• Do shut up when the house lights dim and the orchestra starts to play the overture or entr’acte.  Now I know that these are transitional moments in theatre but Jonathan Tunick doesn’t spend his time orchestrating Sondheim’s stunning songs into a beautiful overture so you can have your own personal underscoring.  Remember, those are live actors at work up there.  This is not television.  Zip it!
• Do stay through the curtain call.  These talented folks have just given you their all, the least you can do is recognize it by applauding politely.  There is nothing tackier than seeing folks hauling tail up the aisle before the lights have even faded to black on the last scene. 

DON’TS:

• Don’t take snacks into the theatre.  This latter day practice is déclassé and makes you look like a tourist (no offense to the tourists, don’t send me emails!)
• Don’t unwrap candy during the performance.  If you think you will need something that badly during the show that you can’t wait until intermission, unwrap it ahead of time.
• Don’t use recording devices of any type.  This means cameras, tape recorders, video cameras or any other recording medium.  It is against the law.  Should you violate this law you can expect to quickly be visited by the theatre ushers and the very serious “private dick” checking bags at the door (an unfortunate but necessary addition since 9/11).