It's simple - you need more visitors - and that's the difficult part. To get more visitors your blog needs to be on page 1 of Google for the subject it relates to. If your blog isn't getting many visitors then start another blog about stuff people are looking to buy (either goods or services). If your blog is just a general blog about 'my life' etc.. then it is very unlikely that it will make any money. You need to research backlinks, keywords, SEO to learn how to get to page 1 of Google. I do earn $ from Adsense (around $800 a month) from 12 different blogs - it's not a lot but it is a start - it takes time and perseverance and there are allegedly people making a lot more so I am probably doing something wrong !
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