How can we make stickermule.com better?

My friend and I just finished designing our 1st ecommerce site: http://stickermule.com

Sticker Mule is meant to be the easiest way to buy custom stickers. We also sell [URL=“http://stickermule.com/t/categories/device-skins”]device skins too sorta like skinit.com

We’re new at ecommerce and web design in general. Altho we’ve done print design work for awhile. We’re quite happy with the site but feedback is much appreciated. We just launched 1 month and want to do another round of updates soon.

Any specific weaknesses in the site design? Thoughts?