Something so simple you'll overlook it....

The "Add to Cart button" - probably not worth thinking about too much, you might think... but think again!

That button is your connection to between you, your user and the £££ (or $$$) rolling in. Get it wrong and your site's users will not touch it with a bargepole so it might be wise to take a look at a huge selection of Add to Cart buttons to help you get creative:

http://www.getelastic.com/add-to-cart-buttons/