Your blog should be about whatever it makes sense for you to talk about. Write about your company, your products, how you come up with your ideas, specials and sales you have, your policies and rules anything that will help people understand your company better. Talk about the competition if it makes sense to talk about them. Don't ever bash the competition, since that never does anyone any good, but compare and contrast a "they do it that way and we do it this way" kind of thing. I don't think you should give excessive publicity to those who are in competition with you, but you don't have to pretend they don't exist either. Just stay open to what is happening around you, and your blog topics will start to naturally flow from the events that occur in your day.