I just advertise for local metal bands, personally

Layers, patterns, gradients, and screen printed art, mostly.

Lots of screen printed art. I’m a big fan of mashup designs where two or more IPs are mixed, like star wars and star trek mixed and represented as chibbi cartoons, basically just someone’s fan art on a t-shirt or sweatshirt, such that you aren’t really advertising any of them as its not immediately clear what’s even on it. Also just art I like. Tons of places to get stuff like that. I also have a lot of shirts with jokes and phrases and the like.

Layers are good if you live somewhere that isnt too ridiculously hot, plain or gradient base t (or one of the more basic screen printed shirts) under a contrasting over-shirt is good. Really opens up the options because basically anything button or zip works, patterns or solid colors, and the extra fabric layer hides a lot of imperfections.

I do a lot of thrifting, especially when I travel, because the variety tends to span different styles and eras and people buy stuff online that ends up there, but it takes a while to really build up the wardrobe that way.