Hi Konstantinos!
First, Welcome to Etsy - your Shop is lovely, great photos. It is not unusual that you do not have sales yet, it does take time and first sale is different for everyone. Here's some hints since it is extremely important that your seo will get you found in customer searches.
Google searches look at your titles and descriptions.
Therefore, your first sentence of your description should repeat what your item is as in your title - you can rearrange the title words around and add more words - it does not have to be a gramatically correct sentence, just use important item keywords. Then go to explain your lovely item.
Etsy searches look at your titles and tags.
So you are found by your titles, tags, and descriptions. If you were a buyer looking for items like yours, what would you type into your search? Ask some friends - family what they would search for - it is amazing how we all think differently.
For example - I might look for "silver pendant, silver necklace, pendant on cord, heart jewelry, heart necklace, Tolkein jewelry, Hobbit jewelry....
Feel free to ask away!!