Low CTR can be effected by the ad format you are using and location of your banners. For example, pop ad format, get 100% CTR. Banners get lower CTR than Pop traffic as not all users are clicking the banners. Also there are banners that works better on different places, therefore it’s important to places the right formats in the right location.
Most important thing in order to get higher CTR is to increase the volume of traffic we usually work around 5K imp.