The BBC synopsis for the episode follows, which might be considered a spoiler:

The God Complex: Trailer, BBC, via the BBC Doctor Who site - may not play outside of the United Kingdom
There are also three preview clips available from the episode:
The God Complex: Preview 1, BBC, via the BBC Doctor Who site - may not play outside of the United Kingdom
The God Complex: Preview 2, BBC, via the BBC Doctor Who site - may not play outside of the United Kingdom
The God Complex: Preview 3, BBC, via the BBC Doctor Who site - may not play outside of the United Kingdom
The BBC published an interview with writer Toby Whithouse; plus, Arthur Darvill provides an introduction to the episode and on working with guest star David Walliams:
The God Complex: Arthur Darvill introduction, BBC, via the BBC Doctor Who site - may not play outside of the United Kingdom
A number of publicity photographs for the episode have now been released:
**** PUBLICITY PHOTOS FOR THE GOD COMPLEX
**** MIGHT BE CONSIDERED SPOILERS