SEO isn't as intimidating as it seems. :) I looked at your shop and here are a couple suggestions.
1. I wouldn't overpopulate your listing titles with keywords. For example, "Polar Bear Christmas Card, Merry Christmas, Happy Xmas, Animal Card, Holiday cards, Winter collection, Blank inside, Digital Illustration" could be shortened to "Polar Bear Christmas Greeting Card". Maybe make your titles sound like something people would actually search for? Think of how *you* search for items. If you were looking for a card with a polar bear on it, you'd probably input something simple like "polar bear christmas card", right?
2. I can't see how you tag your listings, but since you're limited to 13 tags, you could do this little trick. Keeping with the polar bear card example, open etsy in a new browser window and type in the search box very simple terms, like "greeting card", or "seasonal card", and see what pops up in the little "suggested search" box. Those will be your most popular search tags. So I just typed in "polar bear" and got things like "polar bear necklace", "polar bear earrings", "polar bear cake topper", etc as more specific searches. I wouldn't tag your greeting card with an earring tag, but you can see what I mean by popular searches and tags. You want to use some of the tags you KNOW people are looking at to describe your item, so there's a better chance of it being found.
3. Something I learned from elsewhere, don't do single word tags. Tags like "blank card", "polar bear illustration", "holiday greeting card", or "winter illustration" would be good.
4. You can check up on the effectiveness of your Etsy SEO through your Dashboard. Go there, and click on "Stats" and look at the traffic sources. If you have "Search" at the top of your Within Etsy panel, that's good, and that means your tags are strong.
There are plenty of Etsy SEO resources online, too.
http://marketingartfully.com/2015/09/16/seo-for-etsy-sellers-ultimate-etsy-seo-guide/http://www.instructables.com/id/How-to-Sell-on-Etsy-Etsy-SEO-Tips-to-Get-More-Traf/