What is SEO
Search engine optimization (SEO) is the process of improving the visibility of a website or a web page in a search engine's "natural," or un-paid ("organic" or "algorithmic"), search results. In general, the earlier (or higher ranked on the search results page), and more frequently a site appears in the search results list, the more visitors it will receive from the search engine's users. - Wikipedia
So, what is the most important step for Search Engine Optimization?