There is a lot out there in way of articles about how to be successful on etsy, but from what I've seen it boils down to:
1. Accurate price point, around the same as your competition. Too cheap and people think there's a catch; too expensive and they will just buy from someone else. Personally I LOVE when vendors offer free shipping. Sometimes the shipping cost can make or break my decision to buy from someone.
2. Really, really, really great communication. I have seen more rants about sellers who only respond during certain hours, sellers who don't respond on the weekend, sellers who don't respond at all, sellers who take three days to answer a simple question.... Etc.
3. Accurate, good photos. And lots of them. Show angles, use a clean background to show details, use other objects to show size, close ups when necessary, full size shots as a must.
4. Strong descriptions. My biggest pet peeve is vendors who copy and paste the entire lengthy description so that it's generic to all their products instead of specific to the one at hand. Use the same fabric for two dresses? C/p just that info! Include measurements, weights if applicable, materials, allergens if applicable, care instructions if they're going to surprise a buyer, etc.
5. Timeliness. I've also heard a lot of rants about products that were "sent" but never received, or sellers who were constantly asking for "just a few more days" to finish an order. Most people pay using PayPal (is there another option?), which I believe has a standard 45 day dispute time. As a buyer, I want to receive my products, at the worst, within that window. Because PayPal won't let you file a dispute if the vendor can claim to be working with you and just not finished with the product. It's a pretty common scam, actually. I've seen it a lot with custom stuff like wedding dresses, maybe a thousand dollar dress, it never materializes, but by the time the buyer expects to receive it, it's too late to file a claim.