As you will be aware one of the key aspects of Search Engine Optimisation is links, one of the things Twitter and Facebook are great at is linking. If something you tweet is popular and it contains a link back to your web site it is likely that link will find its way onto a 3rd party blog or web site building up your back links. Conversely if your web site performs well in natural search and you post a popular article it is likely that this will get tweeted or added to Facebook, again completing that circle of linking and popularity.
Therefore the key to getting this referral engine to work on autopilot for you is by ensuring you write about things that are remarkable and therefore linkable.