At last weekends Official Doctor Who Convention, the two most highly anticipated panels were the 'Meet the stars' panel and the 'Doctor Who Uncut' panel. The latter of them two featured Steven Moffat (Lead Writer and Executive Producer), Caroline Skinner (Executive Producer), Andy Prior (Casting Director), Michael Pickwoad (Production Designer), Julian Simpson (Director of The Rebel Flesh/The Almost People), and Stephan Pehrsson (Director of Photography) and was hosted by Barnaby Edwards (Dalek Operator). 
With an accent have highlighted the main topics for discussion which you can see a little of below: 

• Moffat said that at times he can see just by a look in their eyes that they get the pitch, and are already thinking of their story. For example, Chris Chibnall (Writer on “The Hungry Earth”/”Cold Blood”, the Silurian two-parter from Series 5) merely had to hear the title before he was on board and letting his imagination run away with him.
• The process of casting can be quite lengthy when it comes to the big roles of The Doctor or a Companion, because obviously there is so much riding on their choices. For Amy and Rory’s replacement the team started looking in October 2011, but only signed the deal with Jenna-Louise last week.
• The Western episode that was featured in the trailer was shot near Amarillo, Spain on a set used in a lot of the spaghetti westerns.