There are a few ways to drive traffic to your store. Here are a few tips to get you started:
Add descriptions to your products and store. If your store and products do not have accurate descriptions then customers will not being able to location your products when searching. You might have the best cat shirt the world has ever seen, but if cat doesn't exist in the description or title then it becomes much more difficult to find it.
Tag your designs accurately. When uploading your designs, be sure to tag any and all relevent words or short phrases that describe your art and don't forget to add at least one category to your design.
Social Media! Use Facebook, Twitter, Instagram, Pintrest, Tumblr, etc to spread the word. Keep your fans up to date!
Tell your fans. E-mail them or shout at them, but let the people who love your art know where to get it.
Blogs. Contact some bloggers and let them know you have a cool tee, phone case or art print coming out.