What are you passionate about? What excites you? What do you love doing and talking about? Those are the things that would make a great blog.
It's pretty easy to start one using a service like Blogger. WordPress. or Squarespace. All you have to do is sign up, pick a template, and start writing. I recommend focusing on two things with each article make it informative and make it entertaining. I find that articles that manage to do both, mixing information with interesting anecdotes and stories, are the ones that grab me, no matter what the topic.
So, how do you make money here? There are many ways. You can put advertisements on the site using Adsense. You can put affiliate links to Amazon on the site. If you have a lot of writings, you can bundle them into an ebook. You can also use the blog to promote other things you're doing, like the other ideas in this article.
Each of those things has the opportunity to earn you some real money.