They mostly know what to wear - something a bit dressy or artsy or chic, yet casual (this is a casual age) and, pragmatically, with some sort of wrap so that they can adjust to the venue's air conditioning or failure thereof. No, the audience knows what to wear... except You! There! Dress up a little huh? This ain't cleaning out the garage! Dress for Art please.
No, this is fashion advice for theater designers.
I've learned: never wear anything to the theater at anytime that can't to get paint on it.
If I do wear good clothes - even for an instant, even for a non-painting day - I am inevitably doomed to paint. Or to rip, tear, stain, or otherwise ruin whatever I'm wearing by some other means. Most recently, on an I'm-just-carrying-stuff day, I ripped a favorite dressy shirt. Every pair of my "painting shoes" started out as "good shoes." Ditto my jeans. I wait for the first paint on new jeans with the same fatalism that new car owners dread The First Scratch.
Wear jeans and accept a few splashes and rips as a badge of artistic virtue. (No need to pay extra for 'em at those fancy fashion stores. In fact, be sure to sneer as you pass their show windows because your paint and rips are for real.)
Wear only designated "paint shoes" when painting. (I go barefoot if I've forgotten them.)
Shirts? I wear worn-out dress shirts gifted to me by family, but the very best solution if you want to spent a few bucks, are thrift store Hawaiian shirts. Don't ruin vintage or gorgeous shirts obviously (those are dressy wear!), but you can ruin ugly ones with a clear conscience. The wilder patterns will disguise enough paint splatters that you can even go out for lunch decently. My all-time favorite was a bright red grocery store Aloha shirt with dragons on it!
Aloha shirts - public domain photo from Wikipedia, taken by Vera & Jean-Christophe
* Another nice photo of glorious Aloha shirts HERE.