The folks over at ClickEquations compiled an amazingly comprehensive list of PPC and Adwords testing resources, which I’ve only just learned about. It’s called, appropriately, The Ultimate List of PPC Ad Testing Resources. It’s broken down into three categories: testing and measurement, copywriting, and presentations.
Not surprisingly, your ability to write effective text ads plays a dramatic role in determining how many people you can reach and whether they’re the right type of customers. Yet, even the most seasoned marketers would fail at guessing which of their ads will be successful. That’s why PPC ad testing is fundamentally linked to profitable campaigns.
Great stuff to read there!

One of the great things about PPC advertising is that you can test multiple versions of your ads. I like to write a whole bunch to see which ones get the most clicks. I deactivate the duds, then write new ads which are variations on the winning ads. Sometimes I only change one word.