We do this by prototyping a lot of ideas, iterating quickly, and (ideally) killing readily. All as fully remote company. People in the company have talked about the details of this procedure publicly before, but I took a shot at it when asked to speak at Falmouth University the other week. The presentation (~30min) and Q&A (~20min) were filmed, and can be watched for free here:

http://onair.falmouth.ac.uk/Mediasite/Play/28dd23b44a3c43abbd60ecb6d49969bd1d?catalog=0a29d6d3-1b0b-405b-8976-0d080ce607e8

Here’s a direct link to the slides:
https://docs.google.com/presentation/d/1cCpuFpduP3NX2ZxJY_QaQ_eYxdwKug1tpkkiROI5Xyo/pub?start=false&loop=false&delayms=3000#slide=id.p

And here’s a similar (but longer) presentation by Daniel, David and Ryan at GDC 2013:
http://www.gdcvault.com/play/1018263/How-to-Make-an-Original ($)

Hope you find it interesting!