Depends where I'm going or who with...but generally I'll go for blackshorts over blacktights and a tank top, or another pretty top and heels =]
As others have said, always heels (usually my black court ones- they're like 3 inches and so comfy).
Usually a dress- I have a couple of "Rare" dresses, Topshop bodycon dresses, 2 plain little black dresses (I love dressing these up with accessories), a new motel dress.
Or a skirt and plain vest/boob tube. I love my bodycon ones from Topshop and River Island do some really pretty patterned ones.
I find ASOS can be really good for going out dresses. Plus you can often get something cute and cheap from places like New Look.
Ooh I love getting ready to go out haha!