It will be split into two parts, one in spring and one in fall.

River Song will return, and we'll understand more about her and who she really is.

The "Silence" will return, and will be the overarching villains.

The Doctor will have a clone in at least one episode.

The Doctor will wear a Stetson and trade in his tweed jacket for a longcoat in at least one episode.

The first episode will be called "The Impossible Astronaut", and it's the first of a two-parter. The second part is called "Day of the Moon", if I'm not mistaken. River Song will be in these episodes, and they will be filmed in the American west.

A "gray" in a suit will appear.

The Ood will reappear.

Cybermats will reappear.

One episode will feature "the scariest monsters yet".

Craig, from "The Lodger" of series 5 fame, will reappear along with the upstairs time machine that was also in that episode.