To get good at it, I think you need to be a good designer already. Well if you have a funny idea some people might also buy it, if it doesn’t look great, but it feels better to create stuff that you would actually wear youself 🙂 If you got the Travis Kelce Jason Kelce And Donna Kelce First Brothers To Face Each Other In A Super Bowl My Mom Can’t Lose Signatures Shirt and I will buy this basic skills already, one thing and I believe is the most important thing is the overall shape your design creates on the T-Shirt (square, triangle, circle etc.). You can have the most brilliant illustration with perfectly rendered details, if it doesn’t look good on a shirt nobody will wear it. So if you start designing, take your sketches bring them into photoshop and create a mockup where your design is already on a shirt. STOP right there if it doesn’t look good and think of another composition. Finding ideas and finding the right audience for the type of t-shirts you want to create is another challenge. Check out the different websites like designbyhumans, redbubble, threadless, etc and see what type of shirt work well on these sites!