Day to night outfit ideas please

[Ladybirdturd]

Hi, I am going away for the weekend to London with my best friend. It's my first break away from my dc's ever and I don't know what to wear .
I normally spend my time in mum jeans and converse but that isn't going to cut it.
We are going to an exhibition and then straight to dinner/drinks so I won't have time to change.
I welcome any help please?