An often over-looked factor that is not really considered SEO a lot of times would be keyword research. Most people skip this step because they think what matters is working with the site that they currently have and figuring out how to rank for what they are already going after.
The problem with not researching your keywords is that you may be going after stuff that is probably not worth spending your time trying to win, or even worse, it never gets searched. Picking the right keywords will make all the difference with your optimization strategy. Why even spend any time building links or writing content for something that will never payoff? It is much smarter to properly discover the areas of greatest ROI and move forward with those.