My first instinct would be to select all the apps that have my size format, and then to see which ones are performing. But to get all the apps included, I get the impression that I'd have to have a relatively high CPM to win some of the quality traffic, and this might just end up bidding on some of the low quality traffic anyway with my high CPM. It also feels like I'd need a large starting budget to test out the entire network this way, and eventually hone down on the apps that work. The other way would be to select a few individual apps and to keep adding on, but I don't have information on the best practices of choosing apps for our particular ad (trying to get users to receive a coupon.), and I don't seem to be able to set individual bids for individual apps without creating many campaigns. Do you have suggestions as to how best approach this?
The answer depends on your situation: You could be a start-up that is more concerned with not blowing tons of money, or you could be in a rush to be done. In both situations, your objective is to find inventory sources that work quickly and then massively scale into those inventory sources. I am going to assume that the goal is to be efficient. In this case, I would start with relatively few inventory pieces and a pretty low bid.
The goal of your experiment is to determine what inventory DOESN'T work while spending as little money as possible. By concentrating your spend on a few pubs, you can get to significant results quickly. If you spread out your spend, you won't generate enough clicks or backend actions per inventory source quickly enough to determine if one is actually working. (In my latter user persona, you can simply spend gobs of money to get significant results on lots of inventory quickly.)
So the moral of the story is that you want to get to results, you have to scale the number of pubs you work with to align with the amount of money you are planning to spend. You would like to, within a day or two, rule out bad inventory and focus on new inventory, or alternately, make massive investments in working inventory to print money for yourself.
I would be happy to do a call to further discuss.