Easy: black skinnies - jeans or faux leather, black tshirt, black boots or booties. If the weather is warmer, just that. If it's chilly, I'd add a few layers - mostly black and/or grey - like a scarf, cardigan, and/or faux leather jacket.
Accessories: Black hobo bag with metallic details, a few dangly necklaces, simple stud earrings, and lots of rings. Finish it off with smoky or winged eyeliner and nude lips. Maybe a pop of color on lips if I'm feeling adventurous.
Coincidentally, this is basically my ideal wardrobe with a bit of purple, plaid, leopard, and polka dots thrown in occasionally
Apparently I can't post pics yet, so here are a couple linky links to outfit images I think express this look really well:
Summer
Winter (minus the neon bag)