Book the Forbidden City the evening the slots open, seven days out

Tickets are real-name, so you need your passport number, and they are released at 20:00 seven days before the day you want. Weekend slots go in minutes; midweek is calmer. The palace is closed on Mondays.

Everyone enters from the south, at the Meridian Gate, and comes out at the north. If the day you wanted is gone, walk into Jingshan Park across the road instead: the view down over the roofs is the photograph you were going to take anyway.