If you want to have a little luck, here are some things not to do in a theatre. 

Do not wish another actor good luck - instead say "break a leg." This comes from "bending a knee" (for taking a bow). 

It is bad luck for an actor to receive flowers before the play begins, though flowers given after the play has ended is considered good luck. 

Only fake flowers will be used on stage. Real flowers must be replaced too often because they can't get enough light, plus some actors may be allergic to them. 

It is unlucky for an actor to knit while on the side of the stage. This is because knitting needles are pointy and can rip expensive costumes, or the needle may fall on the floor and cause someone to fall onstage. 

It is unlucky to use real mirrors or real jewelry onstage. Why? Because both items can cause problems with the onstage lighting, so fake mirrors and jewelry should be used. 

Before an actor takes the stage for the first time, it is good luck for him/her to be pinched for luck. This comes from the old wives' tale that pinching is good luck. 

It is considered bad luck to speak the last line of the play anytime before opening night. This is because a production is never complete until it's performed for an audience, so the completing line of the play shouldn't be spoken before an audience sees the play. 

If an actress trips on the hem of her dress, she should pick it up and kiss the hem for good luck. 

You should not whistle while you're in the theatre, especially in the dressing rooms. It is said that someone will soon be out of work if whistling occurs in the theatre. 

Actors are very superstitious about ghosts and the theatre. Most theatres are reported to have at least one ghost roaming about. Monday night is considered Ghost Night. Most theatres don't have productions on this night so the ghosts will have their own night to perform their plays.