Write regularly; not too often or too rarely. Two to three blogs a week is a good frequency to maintain. Depends on the genre though.
E-commerce bloggers must carefully write keeping their audience in mind. Everything you post on your blog will speak for your product or service. Your interaction with bloggers in comments and otherwise will give you a direction.
Blogging is more about you writing your experiences than what readers want to read. To get the right audience, follow your heart and write what you actually go through.