Here is some useful information about the SEO Process :
Search engine optimization is a process of optimizing the website content, linking structure and increasing the back links to domain.
To get listings in top results of search engines search engine optimizer need to apply various on-page and off-page SEO techniques to the homepage and inner pages of the website. But as this process is natural process of driving the traffic it takes time to get top ranking in search results of search engines.
As compare to other forms of advertising SEO is bit slow to drive the traffic in short run because to make the changes in the site content, linking strucutre etc takes time and search engines also takes their own time to crawl, index and store the website changes into their database. Though SEO is slow process, it is the best way to drive the traffic not only from various search engines but also from various well known directories and websites.
The most important & major benefit of SEO campaign is website remains in top listings for long duration even if webmaster stops on-page & off-page process. Optimizing only 20 important keywords will help you to drive good amount of traffic from thousands of key phrases.
I always suggest the webmasters to promote the site in natural listings of search engines by applying SEO techniques instead spending huge amount on banner campaigns & sponsered text ads. As per the analysis done by various advertising professionals, people mostly click more on natural listings as compare to sponsered text ads becuase they get relevant results against their search query.
In short SEO is best way to drive the global traffic from all search engines and it is most economical & useful advertising solution in long run.