Sheer skirts are a flirty edition you should definitely be adding to your wardrobe. I don't quite mean sheer-sheer, where the fabric is completely translucent. But skirts where the fabric is semi transparent are often very light and perfect for summer weather.
Most of the time with these sort of skirts, you'll find that the deign has a definite iron on feel with a lot of antique looking flowers and a clenched waist. The raised texture of the thread creating the floral patterns looks very vintage, and helps give it a little shape. The weight of the thread helps give it some shape, unlike something more flowy.
This features means that sheer skirts are great for semi formal events. Obviously they're not completely black tie, but paired with the firm waist, they make it obvious you're not treating the occasion as lightly as a barbecue.
Pair it with ballet flats and they'll make you stick out enough amongst people who usually go for a one color toned outfit for semi formal events while still looking cute and demure.
In order to get the best effect, go for a floral design with more than one color, like the one below.