Continuously switching Ads around until you find the sweet spot that generates the most revenue is quite important in my opinion. The same goes for testing different Advertisers and advertising methods (CPA, PPC). I'm testing some CPA offers from Peerfly at the moment and I'm surprised by how huge the difference in revenue is when you're using the right banner/offer. Sure, I lost some time and clicks with the testing but in the end it's totally worth it. Do you play around with your ads?