SEO practices recommend that you post about everyday on Facebook, Twitter, and other social media, but what are you saying all that time, and who is listening?
There isn't really that much you need to say after you have built an entire site that is devoted to getting out all your pertinent information. So what is everyone talking about? Well, mostly it may be updates to their site, or business. This is a great way to generate interest - post news about your business, no matter how insignificant it may seem, it is news to anyone that is interested in you, and it just may get them curious enough to continue looking.
Or perhaps you have a huge site with hundreds of products.. then you may want to post your latest updates on your home page, this keeps the info fresh in search engines, and also lets visitors know what has changed, so they dont have to search your entire site.
But what if you don't make frequent updates to your business or site? Well, then you may want to simply talk about related items, what other things are your clients interested in? If you sell sporting goods, it could be as easy as talking about sport teams and statistics... If you sell computer parts, then you may want to discuss the latest news in technology, or different ways you can assemble your parts into various types of machines... there is always something to talk about.
One of the cardinal rules for SEO is that it needs to 1st benefit the user and 2nd benefit the search algorithm. Trying to fool and cheat the search indexing system can have adverse effects.