1. Retargetting with Perfect Audience[0]. The idea is that not everyone will buy from you when they first visit your site, but by showing them some ads after they do you increase the chances that they come back and buy something. These people are especially useful to target because they have shown interest in your product.
2. A/B Testing with Optimizely[1] or a PHP equivalent such as [2]. If you want to update your site to increase conversions, A/B testing is probably the best way to do it. Basically you just want to propose new changes, then test them alongside your current site to see which ones perform better, then go with that one. This one is tricky though, because without enough traffic to your site a/b testing is a lot less reliable.
[0] http://www.perfectaudience.com/ [1] https://www.optimizely.com/ [2] http://phpabtest.com/ - I haven't ever used this so you may want to do some research yourself.