Talk about the design as if you're describing it to someone, and try to think of stuff that is related to the design.
For example your "Made in the USA" design description can rant about cheap products made in China and/or appeal to patriotism. "Proudly announce yourself as an American with this unique shirt." That's something else to emphasize, the uniqueness of the design... "an original design by Sam's Smiles, not available in retail stores"
Your "Made in the 80's" and 90s designs descriptions can talk about those entire decades. "Relive the days of bad pop music and 5 pound brick cell phones in bags" or whatever the 80's brings to your mind.
Keep it to things people would search on. Think about it this way. If you were looking for a direct competitor, someone who had the same kinds of designs, what would you be looking for?
Diane Blackman
Experiment! Try things! Then if you can't figure it out - ask. Play with Your Dog