A lot depends on your figure.If you want to get the most from a lesson pants are better than a skirt that comes below the knees.Tights are better with a scarf around the hip area. The teacher wants to see what the ankles legs and thighs are doing and to see if you are not on straight knees. Ankle warmers are out.
For men to be in one colour , black is better. The teacher likes to se the outline .A white shirt and black trousers are not the way to go.