Google has such a large share of the market that when we speak about Search Engine Optimization (SEO) we are really discussing how to get to the highest position possible when a potential visitor does a Google search. This does not mean we ignore the other search engines but it makes priorities clear.
Google updates their methods on a regular basis. There are 2 main things you need to know: The first is to provide the user with the best possible results. This is defined by Google. They create the rules that they think makes sense to the user and within their business model. They display the page with their preferred listings to optimize their revenue.
The second is that Google does not like when people use techniques that fool their algorithms determining page rank. When they make a change to their methods they do so to improve the results. Doing this invariably penalizes those that they consider cheaters, sometimes banning them from search results. For others, these updates make dramatic changes to where you are positioned in the search.
Because of this, I believe, that working within Google’s rules provides the smartest way to run a SEO program.
Here are links to Google’s SEO Rules: