Of course this is just my own personal interest, you may be a keen amateur photographer, a budding cake decorator or want to write about travelling across Australia. So, carry out your research online by looking at different websites in Google and even on social media sites such as Facebook or Pinterest to see where the money making niches are, where the people are and if these niches are growing or shrinking. It will save a lot of heartache later down the line.
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.
Once you setup your account on AdSense you will be given a code to add to your blog. This code will automatically display advertisements on your blog from companies who are part of Google’s advertising network. You may see ads from small companies related to your topic, or you may see ads from large companies that are completely unrelated to your topic.