First of all, 12 hubs means nothing seriously. I have 60+ hubs and my adsense isn't growing much. Adsense is not a get rich scheme nor you can earn alot of money through it.
You heard many people saying people earning 4-5 digits from Adsense? This is because they have about 10,000 views per day or so.
Now, you can't really get more clicks on Adsense as it all depends on what you are writing and if the ads attract people to click it.
Good luck and keep writing.