Relying on Google for your daily bread (or in the 21st century, targeted traffic) is a slippery tactic at the best of times. In 2012, many sites were savaged by Google’s legions of fussy Panda’s and Penguins – some lost practically all their traffic overnight, as Google believed they were indulging in SEO tactics that were not done in the right spirit.
In 2013, you may well need to change your SEO practices as SEOMOZ points out in their article, The Top (One) SEO Tactic For 2013. The title is a little deceptive, as there are multiple tips collated under one generic tactic. The major tips include diversifying anchor text and links, get traffic from multiple sources and methods among others.