With all due respect to Microsoft's Bing, Google is still the king of search sites. The ranking your website has in a Google search can turn it into a virtual Disneyland or a ghost town. The sites it shows you in a search can mean the difference between finding that important information or going off on a wild goose chase.
That's why Google's ranking system is so important, and complex. It uses hundreds of details about a site to figure out how useful the site is and where it should go in the rankings. However, there are some main features Google has focused on over the years.
Naturally, there are companies that try to tweak these features on their sites to game the system and get as high as possible in the rankings. In the early days, this meant lots of "important" keywords on the page for Google to find.
In response, Google moved away from keywords and focused more on links. Sites that were linked more on other sites were thought to be more trustworthy. So, companies started setting up link-sharing systems to fool Google.
Google then added a focus on well-linked sites that update often. And that's where we're at right now.
Unfortunately, this means that heavily updated websites with a lot of misinformation can easily get to the top of the rankings if enough people post it on Facebook or link to it in blogs. That's why Google is about to change things again, and this change is a doozy.