As a followup to this question, I'm setting up DFP for a blog and need to show one set of creatives to users from the US or UK, and just let AdSense fill in that ad unit when the user is coming from outside the US or UK.
I've been playing with DFP and the interface isn't terribly difficult... I have already defined my ad units and uploaded creatives. (I also understand how to set placements to geotarget.) However, I'm not sure how to put the pieces together-- for example, I don't know exactly how to configure DFP to use adsense ads when the geotargeting doesn't match US/UK. Can someone give me a brief step-by-step answer to accomplish this goal?