Search Engine Marketing: Test Those Keywords
You’d never run the same mailing with the same list, but there are a number of marketers who never change keyword buys or landing pages. Use the same rigorous testing online as you would offline. What kind of testing you do depends on what kind of data you’ve got and what your resources are. You want to focus on areas that have the greatest yield with the smallest investment. If you have keywords that could be higher in the results if you could afford it, these are the ones to test optimization first. If you continuously test the most important things, you may never need to focus on smaller, more insignificant things.
—Kevin Lee, founder and executive chairman, search engine marketing firm Didit.com