Writing for income is a great idea and you can use your blog to showcase your skills for potential employment. I'm still far from getting on the road myself, but I have a foot in the door in the writing area (poker and gambling news), and hope to make that a decent base income for the future.
I recommend that you Google topics on writing news articles to get a feel for the format; then if there is an industry you're passionate about, you can find a topic and write about it on your blog to get experience. You don't necessarily have to break an exclusive story, but you can put an existing story in your own words with a unique angle (trade journalism).
Here is a good article on writing for the web.