Since I'm still new to all of this and have only had 15 sales so far I haven't had any repeat customers just yet, but I'm hoping to get some soon!
For my last 4 orders I've been including a Thank You card with a little hand written note thanking them for their purchase and offering them a coupon code for 10% off their next purchase in my store. Not sure if it will get anyone to buy again, but we'll see. Couldn't hurt, right?