It's boring and old news, but your most useful advertising is your Title, because that is what encourages the eBay buyer to open YOUR listing.
You have 82 keystrokes to grab his attention.
The first four words are considered the most important because more than half of buyers are using a phone and that is what they see.
Second, eBay tells us, are the Item Specifics, which are meant to get our listings on SEO (that's really just Google). The more of them you can honestly give, the more likely you are to be found in a Google Search.
Old time sellers are dismissive of IS, because they are a lot of work. But if eBay is right about Google, they will work for us.
Personally, I like the older version of Promoted Listings, where I chose the fee I would pay and only paid it if the item sold. I saw a huge bump in the number of Views, and while I don't think after nearly two years I have paid out more than $50* in fees over four selling accounts, my sales did jump. I believe PL brought viewers to my items and while they may not have bought the promoted item, they found other things they did want. I use it on all of my selling accounts now.
Social media are fine for chatting with high school friends you haven't seen for 20 years, but unless you can get thousands of followers, your presence is just a drop in the ocean.
*YMMV- I chose one percent , I'm not a huge seller, and my items are very cheap. I did not use PL on anything over $25.
