adsense getting information from your website, so if you write "gold" then adsense show ads which contains gold ads maybe
You should optimise your web page for high paying adds. This is not so hard. More harder is to get traffic to it. Try google search with "high paying keywords" and you should fine some of them. It is all about insurance stuff, health.....some say that mesothelioma-risk.net has high paying adds.
i have a website where users use their own google numbers and they optimize their space by themselves in the settings . By doing it I learnt a lot
I tried creating a mesothelioma site and didn't turn out as good as I expected, lol. But, one day so far i actually got 1 click that day and it said I made $2.01 from it, but what good is that if i don't make anything the rest of the days of the month. haha
Financial sites seem to get pretty good paying keywords if your articles are good and written well. In addition good financial sites have a tendency to have quality amounts of clicks on google ads in my experience. That is just one "niche".