hey there,
A couple things on this... both Pinterest and Instagram are incredibly useful tools for promoting your shop. If you have the bandwith, I would consider keeping up with both.
The great things about pinterest is that once you've created a board, it can hang out there for a while and still get traction and be shared across the platform. On the other hand, Instagram is something you have to keep up with nearly daily to create a following.
Pinterest is a great place to add more information about your product, and link directly to it. Beautiful photos go a long way, but you can also add in the break-down of how you made that product, which tends to get traction on Pinterest.
On Instagram, the key is beautifully, well thought-out and easy to digest visuals. Not too much information, as people are typically scrolling through pretty quickly. A quirky caption + information on how to find more of your products should do the trick to get you traction on Insta. You may also want to consider following those who have similar interests and engaging with their content -- this will get you noticed and followers.
Let me know if you have any other questions!