There are a few things you can do:
-Improve your landing page and split test for conversions so you effectively get more revenue for the same clicks, increasing your EPCs.
-Improve your ad copy and split test for CTR/Conversion rates to get a higher quality score and higher conversions (the two are not directly linked). This will also increase your EPCs and possibly lower your CPCs.
-Optimize your price points. Some price points obtain higher conversion rates than others (Eg. 50 vs 47). Although if you don't own the product you are promoting this could be tough.
-Optimize the backend of your system. Adding upsells, downsells and cross sells to get more value out of your customers. This will also let you pay more to obtain a new customer. Again, provided you have control over this.