Hello, I think there are many common things you can do to improve sales but it does depend on your competition. I've found it helpful to go through each competitors website and compare features and services to my website. For example, how does price compare when someone finds my site in the search results vs others? How about shipping/delivery? Do others promote free shipping, and I don't? Do competitors have a 800/toll free number, and I don't?
One example, that comes to mind, is adding live chat to your website. Another, creating an email subscriber list that allows you to pursue leads and keep your business in mind with potential customers.
There are always way to improve. And when in doubt, test ... test ... test.