Is this a night time event? I'm kind of assuming it's happening later on in the day.
High heels definitely. Don't do flats. The high heels will instantly dress up the outfit.
For shade, I like contrasts, so I would pair the jeans with a punch of bright color (like magenta) with your dark denim. But you can always go with shades of grey too. Just don't do black, that's a bit on the boring side.
In terms of the style, you can even wear a tank top. It all depends on how you dress it up!
Of course, depending on the simplicity of the top, you may want to jazz it up with some metallics in your jewelery too.