Try to wear some make up if you already dont, doesn't need to be bold colours, some light pastels will make a difference. Similarly, if you wear black or darker colours all the time try some lighter ones like pinks or greens. I understand how you feel about trousers, and wearing skirts is a big change, but you could maybe get a nice belt, a pretty scarf and other accessories like earrings or bracelets.
As for the hair, you can just play around with hairclips to get a style you want, it doesn't need to be that long to look different and pretty.