Hello, Adrianne!
My advice to You is - think like a buyer not like seller.
Exemple: i don't think that someone will look for "Pop Tart" or "rainbow".
What You would write in search if You would look for a greeting card?
Start with good title and then aptly tags will come by themselves.
https://www.etsy.com/listing/242301266/greeting-card-cassette?ref=shop_home_active_1It's not enough to call it "Greeting Card : Cassette".
I think much better would be: funny greeting card, vintage congratulations card, 80's style card or something like that.
And about tags... they work much better if they are not just one word like "card" or "friendship".