The first thing you will need to know is to decide what subject matter will you write on. This is usually a personal choice. Although some topics may be more profitable it makes sense to write on topics you know more about and can become an expert in the field. You will want to become the go to place for information on the subject your blog is about. If you can get visitors that recommend you to others it helps significantly to be successful. Other web site bloggers will link your site and mention it when they write on the same subject. The subjects you are most interested in you will find it more easy to write about and you may very well be almost an expert in the field before you start your blog.
So, is this a good business to go into? It's a great at home business. You can write when you want to, when your creativity juices are flowing. It doesn't require someone approving your articles. You decide what you publish on your blog. The cost is very cheap to get started from a small monthly hosting fee to costing nothing with a free blog. On the negative side it takes time to make money. Many give up before they make much money. It's a great business, the blog writing business, if you enjoy writing on the subjects you are interested in.