Working with advertising networks isn’t your only option when it comes to selling ads. If you end up with enough traffic, advertisers may come directly to you and ask you to place their ad on your site. You can also contact advertisers yourself. The biggest difference from the above mentioned option is that there is no middle man, which means you can set your own ad rates.
Quality content is content that people can engage with and find useful. Your content should help readers and bring them value. Your blog needs to have interesting, helpful content that people would be willing to recommend or share with their friends. The format, structure, layout (and, of course, the writing itself) will all determine the quality of your blog.