How to fill a blog…  Honestly I let my clients and prospect clients help guide me with that.  When I answer their questions I will grab some of the content (my answers) and post it to my blog.   This is great for my visitors that have the same questions, so it may save me time later on by already addressing those questions, but also for Search Engine Optimization!  The Search Engines just looove all that information, information and information.  So, when you have a blog, consider doing the same, post Frequently Asked Questions to your site, as they come in.
It’s good to add content regularly to your website in small even portions… like a page a day if possible.  It doesn’t have to have a lot of information, but the more the merrier as far as the Search Engines are concerned!  It’s okay to add a lot all at once, but I’ve seen somewhere that it’s good not to add too much all the time otherwise the Search engine red flags go up and they think you may be spamming your site with content…  So gradual content added is most recommended.  (of course you want to get your site filled up with products so I’m not referring to filling up your store – just addressing the notion of after your store has been filled – to keep information coming in – gradually).
There are websites that offer Free content or free articles – STAY away from these sites, the Search Engines have documented their articles and their links and will consider your website a spam website if you post these free articles on your site.  I learned this the hard way… I used to be on the bottom of page 1 for Google with the keywords: ebay store design before I gave free content articles a try.  It has taken me roughly 3+ years to recover because I used free articles to build my site up.  BIG lesson learned!
So again, when you think about adding content to your blog/website, do it gradually and use fresh information or fresh answers to questions you receive (or questions you can think up that someone maybe searching for).  Trendy stuff and beauty news is also great to add to your blog.
Made To Be Unique also offers content writing services that are written uniquely for you, so this is something also to consider when needing content rich information for important pages and posts.