Show confirmation whenever a product is added to the cart
When people add something to the cart on your product pages, what should happen?
Most importantly: it should be obvious they’ve added something to the cart. Clear confirmation.
It’s funny how many sites screw this up either by not displaying a proper confirmation or showing an animation.
It’s also important to keep the mini cart notification/contents open until the user clicks elsewhere, this allows for control as well as the clear notification.