Search Engine Optimization (SEO) is the science of keyword use and placement.
There are many different ways to optimize a website for the search engines and they all are critical for visablity.
Each search engine, i.e. Google, and Yahoo, use their own respective algorithums to assign ranking. There are methods used to achieve desired rank based upon:
Geo Location
Style of site
Site Content
Desired Location (Local, Regional, National and Global)
Just to name a few...
We have included to this site a few examples of what is involved in a full site optimization process. They provide a good start, but there are a girth of opportunities in the optimization process and what would work on site A, may not work the same for site B. Optimization is also more easily performed upon website conception. However, SEO happens to legacy websites* everyday.
*LEGACY WEBSITE - this is a website that is already in exisitance.
The science of SEO