As you can see in the picture above in the outfit I included a loose but covering shirt, a jean under the knee skirt, and sandals. I live in Florida and so this is kind of how I dress if I am staying outside a lot. I love wearing jean skirts because they have shape and you don't have to worry about the wind blowing them up.
In this outfit I show wearing your hair up for half-way up really helps with the heat. If you like wearing long skirts then fluffy or t-shirt material maxi skirts are good choices. T-shirts are nice to wear also but it depends on the color (darker is hotter) and the thickness of the shirt. Airy but covering is what you should go for.