This is a complex question, actually. A lot depends on where you are in your internet journey.
Did you research your keywords before choosing your subject? Did you assess the competition before deciding whether it was worth writing a Hub? If you did, so you know it's a subject people are looking for and the subject isn't saturated, it's worth beefing up the Hubs, increasing the interlinking between related ones, and doing some serious off-site promotion.
If you don't know what I'm talking about, or you think the "competition" column in the Adsense tool tells you how much competition YOU are up against (which it doesn't), then you need to do a bit more study so you can get a better idea which Hubs are worth making the effort on.