For a detailed, polite guide, follow this link to Time Out:
http://www.timeout.com/london/theatre/london-theatre-etiquette-a-guide
My biggest annoyance is people turning up and taking their seats after the performance has begun! Simple fact is it is extremely annoying to people you have to make stand up to get your seat and annoying to people, whose views you block, when doing so! Now I know they may have been a delay in getting there that might be out of their control, but even then, leave plenty of time to get there to avoid turning up late! On the ticket, it states a time. It is not the time you need to there by, it is not the time you need to be in your seat by, it is the time the performance begins! So if it states 7:30pm on your ticket, the performance is going to begin at 7:30pm! So here is a little tip, aim to arrive at the theatre, around half an hour before the time stated. I say this, because half an hour before the performance is the earliest most theatres will allow the audience in to take their seats, but it also gives you time to buy drinks, merchandise, go to the toilet, find your seat and get comfortable! And this goes for the second act after the interval as well!
Next, general noise! Now I will admit, if I am attending the theatre with a friend, my daughter or the husband, or if I have got chatting to the person next to me before the performance, then occasionally I will speak to them during the performance. However, I make sure to whisper and if I am at a musical, which is usually the case, then I do it at the end of a musical number when people are applauding. Noise, otherwise, drives me nuts! Whether it be loud talking, opening a noisy packet of food or even having a irritating laugh, it is enough to ruin a performance for me! The only people anyone should be able to hear and hear clearly, is the people on stage! So shut up, stop opening crisps and keep that laugh to a minimum!
Lines for the toilets always annoy me! Obviously we have no control over the number of toilets and there is always going to be a queue for the ladies, but seriously, it is beyond how it can take some ladies so bloody long in the toilet! I stood in two long queues in the past three weeks alone, with me missing beginning of the second act, breaking one of the rules of the etiquette I have moaned about above. If you are wearing a stupid outfit that takes time to get in and out of, then don't bloody wear it! Get in, get out as quickly as you can because you just pissing off a load of people who don't want to miss any of the show, but don't want to be sat bursting for the toilet! Oh and please don't decide you must go to the toilet during the performance if you are sat in the middle of the row! It is the same as arriving late, you are annoying the people you make move and the people whose view you then block!
Final one for inside the theatre deals with the end of the show and leaving the theatre. Now I will be honest, if I can get end of the row seats, meaning I can be first out at the end of the show, I buy them, but sometimes it is not possible, depending on what seats are left or the website you book them through, meaning there is no control over where you sit. But if you are the person at the end of the row, or anywhere in the row for that matter, don't take forever over leaving. Some of us want to leave as soon as possible, not because we did not enjoy it, but because we might want to head to the stage door or get home as soon as possible or whatever that reason may be. You mucking about doesn't help people like me, quite honestly it just annoys us. You can sort yourself and your bag out once you get outside! Trust me, it is much easier, even when it is winter!
Now for stage door etiquette. Yes, it does exist, especially for those who stage door regularly. For the majority of the shows I have gone to the stage door after, the main cast generally tends to stop for photos and autographs, as they are more than happy to. Therefore, if you go to the stage door, don't block the door, other members of cast, orchestra or crew leave by the same door and need to get past. Next, don't crowd the cast member. For the most part, they will work their way down a line or barriers, but they will get to everyone who is there and waiting! Also, be patient! Depending on the character they play, depends on how soon it is before they are to leave, though I have known those with most complicated costumes to be one of the first out. Even then, cast members may have guests or be meeting with a celeb who has come to see the show. Either way, they will come out and chances are they will stop, unless they are in a rush. Finally, if a star name is currently performing in the show, they may not leave by the stage door. It does not mean you won't be able to meet them as it depends what theatre they are at, but the chances decrease rapidly. If they choose or have to leave by a different door, then there is nothing you can do as you usually find out after they have left.
Last two things, inspired by the Time Out article, it does not matter what you wear to the theatre and if you want to give a standing ovation, even if no one else wants to, then do so!
