The key is getting more traffic. With more traffic comes more clicks, because the majority of your visitors aren't going to click on the ads.
So, the more visitors you get, the more your odds increase that one will click on an ad.
You get more traffic by using good SEO practices and writing original content. I think the best topics are travel, finance and health, or at least that's what I have heard.
Good luck! If you figure it all out, let me know!