There are good plugins to manage this and its not always good to just slap on a couple of large banners.
The problem is with Google AdSense and you would be best going to a related forum really. AdSense has complicated terms that may not register all of your clicks.
You defo should be getting more clicks for 250 unique visitors per day unless the ads are just not interesting enough to visitors. People dont come to a site too click on an ad then leave it. They initial come to it for specific information they seek and then click on an ad because it provide another lead to that information.
This cycle might not be happening and there is not actually a problem? I think ya should be getting more though and interested to know how you get on with this.