Narrow down the topics by reflecting on profitability and other goals. In order to make money, you'll need to find a niche that other people haven't filled already, but is still popular enough to attract a significant number of visitors. Also consider other factors, such as money you'd have to spend if your blog focused on reviewing products that you in turn would have to buy.
Clueless, confused, and confounded with choices, we had no idea how to start a blog or how to be a blogger. When should we start? How do we register a domain name? What is hosting? Which blogging platform should we use? How do we choose a template? What is a plugin? What should we write about? Heck, we could hardly spell HTML, let alone build a blog!
Lets say, for example, that you refurbish and resell used smartphones out of your home. You could use a blog to attract visitors to your website where you list your current phones for sale. Your blog might cover topics about DIY refurbishing. On one level, it seems counterintuitive because you want people to buy your phones, but it also helps you build a brand and gain recognition. Social media guru Jay Baer explains the concept on Copyblogger: