My suggestion is advertise your adsense sites like crazy, make sure you have the best placements for the ads, and keep your site up to date. Most importantly stay dedicated to it and be patient. Time pays off.
Get traffic and try to put ads in the correct place... if ur CTR is above 1-2% i think u are doing great... try to achieve this by different placement options and get high traffic.. thats it I do and I am happy with the results so far
Its also depending on the country from where you got clicks and the cpc of the keyword clicked by the visitors. You have not mentioned your niche. So its hard to predict why its low.
Building more backlinks. That's the key to quality traffic. Search Engines provide the best traffic because of the high CTR. Keep building on backlinks, there are thousands of directories just waiting to get your website into them.
Trying different niches the revenue can be increased. Sites need more and more backlinks to boost up the revenue.