First time tips for Print on Demand

Hello, I am new to print on demand and just wanted to give it a try. I am 17 and don’t have any other business experience but I saw this on a YouTube video and wanted to give it a go. I have opened my Etsy shop and uploaded my first product using Gelato. My niche is mental health because I’ve seen some people at my school wearing shirts related to that. I’ve been wanting to earn some money while I’m in school so I thought it was worth my time. Any tips or advice would be much appreciated as I am still new to this. Thanks!