I signed up for Etsy on the 11th March, and completed my first sale (actually it was 2!) on the 22nd. It was pure luck, I have no idea what helped the sale...and it certainly isn't my photography, I was too impatient to wait, and just threw up some pretty average looking shots!
I'd be interested to hear what helps with sales too, as I consider my first a complete fluke...think I'll be more excited about the third or fourth than the first!! :D