Try new sources of traffic. Or better yet, try focusing on the high-CTR traffic sources you already have. Changing colors, or setting up a rotating colors, can also help boost CTR. Finally if all else fails, play around with the layout. Place ads in places you wouldn't normally place them (as long as it doesn't violate TOS). The great thing about low CTR is that there isn't much to lose.
I have increased my ctr dramatically (to double digit) by changing the placement of ads and blending the ads with contents. If you have sufficient traffic, (especially, targeted and organic) you can increase the ctr by this method. To attract targeted visitors, you require unique and quality contents. That is a must