I like waistcoats for guys, because they take attention away from less than wonderful trousers (and frankly, lanky teen boys can find it hard to get trousers that fit and look good), and also look smart with a shirt that is a bit fuller than usual to allow for arm movement (of course, if you're going the poet shirt route that's different!). You can also wear a waistcoat over a turtle neck which is a handy and budget-friendly solution..and for violinists, a turtle neck is more comfortable than a shirt-collar and tie. Another, less formal approach is to have trousers (e.g. cords) which are a tad looser than usual to give you room to move, and a stunning pair of braces with a loose shirt, open-neck and rolled-up sleeves!
Since I have the opportunity to observe lots of "guest performers" from a conservatorium and attached high school at Viohazard's student recitals, I get to see lots of girls' formal wear! I notice that most of the girls who choose evening dress are actually wearing a fitted top and skirt - looks like a one-piece dress, but allows for a little more movement. Also allows them to replace the long, full skirt with a short, straight black skirt or trou for the ensemble parts of the programme.
Chubbier girls often have a chiffony transparent top over strappy evening wear, which saves having to worry about those upper-arm "wings" suddenly taking flight

...a point that violinists, flautists, and sometimes piano players can feel sensitive about.
...or you could just flaunt your tats!