Fairly recently I have started doing PPC with Bing + CB. I'm a noob, though the results have been great so far, despite minimal testing/optimization. Now I want to scale up and throw more money into the game. What's baffling is that there's so many different variables to consider: kws, their match types, ads, demographics, schedule etc. And then all this multiplied by the number of campaigns. So how do you go about testing your PPC campaigns? Do you try to test one variable at a time, say, which ad works best, and then, once you have the winner move onto something else? Or do you test several variables at once, running many ad groups with different settings at the same time?