The key thing for me is to dress simply with two factors in mind:
a) Freedom of movement
b) Ventilation
For me, I usually wear a nice pair of neat pressed slacks and a nice dark colored t-shirt (always carry a spare or two, a towel and anti-perspirant) and good shoes of course that are comfy and allow me to feel the floor. The ventilation aspect is so vital to me since I do EC Swing, Latin and Hustle, all of which are strenuous (but so darned much fun). It doesn't do much good to be all decked out and yet roasting, dying and drowning in sweat

.
Like I said, neat good-looking simplicity and comfort is my preferred method.

Thankfully, most venues I go to are air conditioned, which makes a HUGE difference!
Hoo Hooooo Hoo Hoooooooo