Repeat coupons don't seem to work for many. Only 2 of my customers have used theirs.
I've found that excellent service/shipping/product helps. Get them to remember you.
Growing my email list has helped, too. I usually get a few people to my shop right after sending something.
Update your shop- renew and list new items. Blog and pin. Keep yourself at the top of your customers' minds.
When you see a product has arrived, send a friendly convo. I like checking in sometimes to make sure their package got to their hands. When someone buys something, I send a thank you the same day. Save a "thank you" snippet. Have all your links at the bottom.