I have spent much time trying to do "what Google wants". I have written weekly blog posts in my WordPress blog since 2006. I have tried to write useful articles for others in my niche and I have been rewarded with loyal followers. Off-site I have only got natural in-bound links from people who like my stuff and I've only ever done maybe 10 guest posts. I also get natural social shares. I have never indulged in any paid links. Ever since 2006 my organic Google rankings and organic traffic has been increasing, as you'd expect as I constantly add quality articles. However, since at least the beginning of the year my organic traffic has started to fall to a point I now have the same traffic as two years ago! This is quite an extreme drop of at least 50% of organic traffic. It looks like I've suffering some Google penalty but, for what, I don't know. http://robcubbon.com Any suggestions?
Have you seen differences between the good times and the bad times when it comes to your bounce rate, exit rates, page views, etc? I would need a lot more information to give you something solid. If those also experienced fluctuations it could be that Google thinks you are nothing more than a big advertisement for the "How To Market Yourself Online" ad towards the bottom of the page. Checking ahref.com I can say that I can see you lost a lot of links into your site in December. You also lost a lot more in the past month. This could be because more and more bloggers that used to link into you with dofollow links are switching them to nofollow in a strategy to stop bleeding pagerank on their own end. Also if somebody mentioned you in a blogging for dollars forum the forum might have changed to nofollow links as well.
Google might not like that you use dofollow links to offsite content that you might not be really trying to give pagerank to.
Your site looks great! But I can see sharp decline in traffic in jan and in apr 2013. In Jan, google did an update on image optimization. Not sure if you were hit by that (well, I was) and not sure what happened in april. May be you can check out if you've spammed your sites/images with keywords. By the way, I read an article on 'Freelancer vs Entrepreneur' on your site. I loved it since I was considering myself a 'freelancer' till now and I have now decided to call myself a 'business owner'. Here's what you said - "Freelancers get paid per hour for the work that they do; business owners can get paid in their sleep." Amazing!!!