I would say the first thing is be clean. fix clean hair into sleek styles, *iron your clothes*. minimal makeup, and maybe a signature piece of jewelry - a nice, simple gold necklace or earrings that go with everything would be a good thing to invest in. i would also not underestimate your shoes - just make sure they're clean and undamaged. and you can never go wrong with a red lip. also make sure your nails are clean and trimmed
all of the above is my own personal opinion of what constitutes elegance so take it with a grain of salt
edit: i also agree with what others have said about wearing clothes that fit. baggy or ill-fitting clothes are not typically elegant. I think it also goes without saying to avoid wearing clothing with graphics or brands plastered on it.
