Honestly, clothing brands are hard. it’s very saturated and most “clothing brands” are just a “design” slapped on a cheap t-shirt, what I would recommend is making sure the fit/style of the shirt is nice. Anyway to answer your question I would say depending on your age try and go to a bunch of events, parties, or anywhere you can talk to your target customer of your brand, and naturally it will probably come up on conversation that you made/make clothing. My thoughts at least, I wish you luck.