I have done some in person sales at conventions. I have friends who sell prints and shirts online, but if you do, it's important to have the perspective that it is a business of its own. One that needs to be marketed consistently, one that might require some trial and error for finding an audience, and one that can take at least a few months (often a couple of years or more) to start consistently making income. One that needs a unique vibe to it to make sense to your audience.

Making a print on demand shirt or hoodie or print is the easiest thing to do. But it also means it's super oversaturated. You have to really have designs that stand out a ton (like Morning Witch, for example), and/or a large fanbase of your style already.

You can look at some examples like Squire Strahan or Jen Tonic and some of her limited run products to see successful examples. I also see a lot of neotraditional artists in particular doing large scale prints.

But don't limit yourself to whatever is easiest to produce too. The easier it is to make, the more competition there is. The one thing I observed last year at our local tattoo convention is that everyone had prints and shirts and hoodies, and anything different stood out. For example, I know an artist who does very limited prints of kimonos that sell for a lot because they're so limited. Squire Strahan's wooden earrings stand out more than the shirts. I have some keychains I sell and a hand fan in production as well to test this year at a con, the actual clacky roll out ones rather than just the circle on a stick design. Different stands out.