I was hoping for "cartesian product analysis" (how can we trim down the exponential explosion of types?), fearing "certified public accountant" and was completely surprised.

We're here to please. :)

Please update the title. When I read "tips to improve CPA", I was thinking about some suggestions to improve certified public accountants practices.

I think that too when I see CPA, except at HN or some other web-related site. Context.

Optimize and test. Different combinations of ad content and landing pages will impact your conversion rates, and thus CPA.

Yup, that's exactly right. Though, there are good goals you can set up to help indicate that you are getting closer. If you set up a Time on Site goal and a Page visits goal, if you notice both of those goals working but no conversion to signup, you know something if off with your call to action in most cases.

Good to setup those indicators.

Much-needed stuff. I'm really loving the overall shift from clicks and backlinks to conversion and Cost per actions. RCS

Right. People try to optimize cost per acquisition (actions) by just focusing on their campaign/ads and miss the other half, their landing page(s). Critical in improving overall performance.