When I started my adsense business, I had only one site - and that site paid me only a couple of cents each day. I cried again the the week after next, and the week after that, but there wasn't any change in my adsense earning. Taking a look at my earnings, I felt little better than a beggar on the street, with only a couple of spare changes in his bowl.
Fortunately, I shortly noticed that it was dumb to be dependent on just one niche.
I accepted that I didn't have the power to convert a low-paying niche into a high-paying one. But I had the power to select my niches. When I ask them how many niches they are in or how many sites they have, the solution is generally 3-4. You see, it is nearly most unlikely to earn from adsense with just one site unless you get thousands of visitors each day. But i presume you don't have that sort of a traffic, right? If you have just 1-2 niches, I am able to guarantee you with 100 pc confidence - you won't be chuffed taking a look at your adsense revenues. If you need to be an enormous player, you'll have to broaden into lots of niches. If you treat it like a business, it'll pay you like a business.
If you decide to do this work yourself, it might take you 1-2 months or perhaps three months.
Another better option is to outsource this work and have people do it for you. Only that may take us towards the pearly gates of the "kingdom of adsense. Niches that you believe would be high paying may turn out to be total disasters. And niches that appear to be hopeless, might turn out to be real winners. I generally say that you can never be one hundred percent sure about which niches would be profitable and which won't. I've come to understand that if I'm going into ten markets, there will be around six that may will be winners. So if I want 300 profitable sites, I must make around five hundred sites.

If you ask me, I feel this is far easier than looking "the best niches". It is just like throwing enough stuff onto the wall and see what sticks. To keep Google content, I had some decent content on each of my sites. Also I am about to tell you something that might make a small number of you feel uneasy. You've got to have heard that you must have tons of content on your website. "Content is king", right? But my perspectives are a bit different here. If you would like to build an adsense business, I believe "content isn't the king. If you put truly good content on your sites, you'll be left with satisfied visitors, and unhappy takings. The one thing that stops you from earing $300 or maybe $500 a day in adSense is numbers.