Like you, I make and sell templates, not so much clothes but more like accessories for clothes. Some buyers like it when you offer the PSD files so that they can customize it to fit their outfits. You might want to try considering offering that to see if it helps your sales.
I agree with all the posters regarding pictures being very important. If the pictures are lousy, the customers will think they are getting a lousy item. I don't alter any of my pictures to make it look better in PS. What my customers see is what they get.
I don't do much advertising. I share a shop with 2 partners and they pretty much do the advertising for our store. They advertise our new releases in their groups, participate in hunts, and hold weekly sales. I once paid for a feature front page advertisement for one month in the marketplace which was a total waste of money. Join groups where they will give you notice rights to send out notices about your product.
Do you have a blog? If you don't, you might want to set one up. You can get one for free. Try using Flickr, tweeter, facebook, anything that will reach the public where you can show off your stuff.