Public booking for Glyndebourne opens on 10 March.
If you want to jump the queues, tomorrow's Daily Telegraph (1 March) contains a special code that will allow you to book from 8am on Saturday 1 March.
I will print more details here as soon as I know them. However I'm not planning to get up at the crack of dawn, and I assume the Telegraph won't post the code online, so your best bets will be (a) check Twitter before 8am or (b) suck it up, go out, and buy a paper.
*UPDATE* reader Michael points out the code is 10578.