Mistake 1: Not optimizing your site.
Mistake 2: Not doing proper keyword research and ignoring longtail opportunities.
Mistake 3: Ignoring local. You’re loco if you don’t do local!
Mistake 4: Spamming, keyword stuffing, setting up link farms and all other forms of nefarious Blackhat deeds.
Mistake 5: Template websites, Site Builders, Freebie websites that are already <airquote> optimized <airquote>.
Mistake 6: Not adding unique content.
Mistake 7: Going cheap!
Mistake 8: Using mass submission software.
Mistake 9: Ignoring social media/networking (Twitter, Facebook, YouTube, Blog etc)
Mistake 10: Not staying current on changes in the industry.
Mistake 11: Jumping on the bandwagon of every single trend that crops up.
You can read the full article, and the solutions at the Search Engine Journal.