Here is some more information on what causes your site to lose rankings in Google.
Over Optimization of Your Site: Tone it Down a Bit
Not so very long ago, one of the strategies that someone could use to rank a site with Google was to place the keyword that they wished to rank for in several strategic places on the site. So if you wished to rank for search engine marketing in Chandler, you'd create that as a URL within your site, maybe even an exact match domain name. It would also be a category, and the destination page would be peppered with the keyword and maybe a couple of variants. In fact, all you would have to do is create a page with 3-4 lines of text, and then Google would notice you. Things have changed significantly, however, and just within the past couple of years.
With the implementation of the Penguin and Panda algorithms, a bunch of sites all but disappeared from the web. Why? Because the site owners got greedy and over optimized their sites. As a result, Google penalized their site, or worse yet sandboxed them indefinitely. You want to have the keywords that you wish to rank for in your page, however keep the bells and whistles down.
How Google Ranks Your Site
How does Google rank your site? It is actually a fairly complex process. While the automated spiders that search your site eagerly gobble up your keywords, sooner or later, a pair of human eyes will skim your site. Then by a proprietary process known only to Google in conjunction with various algorithms, your site is ranked. If you follow Google's rules, and your site is both relevant and has solid content you will rank higher statistically than someone who over-optimizes their sites, does a lot of keyword stuffing and has irrelevant back links pointing to it. Another thing that you have to know about how Google ranks your site, is that it is not static, it is fluid. In other words, you can reach page one of Google, maybe even land on position one, but you will have to work to to keep your site there, and depending on how competitive your niche is, you may have to fight off a lot of competition. So while it is still important to have back links pointing to your site, they have to be the right sort of back links as well as have a reasonable number of them pointing to your site.
Ultimately, ranking your site on Google is much like a game. If you play by Google's rules and stay up on any changes, you have more than a good chance of getting ranked on Google.