Hum... A few suggestions for you. The first and most fundamental is to try to prevent your ad can run any script, so even if it is malicious it will not be able to do anything, I do not believe that an ad with animations and sounds to be more effective than a simple link or a still image.
Second, you know those ads that offer X but clicking on them you are directed to Y? Avoid them as if they were radioactive. No more annoying thing for a user to click on a picture thinking it will for one thing (the download you want) and actually is redirected to something else unrelated.
Third, do not accept ads of suspicious companies like "CleanMyPC" simply not worth it. It is the main reason I block ads, advertisements that offer really suspicious programs and often try to pretend they are the links to the content I really want to see.