SEO has changed significantly in 2013.
With major updates such as Hummingbird and Matt Cutt’s anti-guest blogging message towards the end of the year left a lot of people confused. SEO work has only become more difficult than the past.
Positionly has created a great info-graphic on the methods that worked in 2013. This should help how previous understanding of the same components of SEO has changed over the course of time.