Today, Pottermore announced that they are going to release tickets for the September 1st viewing of Harry Potter and the Cursed Child Parts One and Two.
Tickets go on sale at 1pm (BST), but clicking here will allow you to queue up in random order. From Pottermore:
We recommend you join this queue just before booking opens at 1pm in order to be in with a chance to book tickets – as the queue is randomised there is no advantage to entering earlier than anyone else before booking opens.
Tickets for this performance is limited, so best of luck!