It looks so difficult, but trust me it is not!
Start with appling base coat to protect your nails. Then apply on a sponge blue and light violet nail polish and dab it onto your nail. You don´t heve to dab it all over, you can leave tip of your nail without colour. Now, take a black nail polish and create shapes of skyscrapers. With a dotting tool or with tooth pick and white nail polish do a lights in window on buildings. For one nail you can create a moon with tooth pick. Also you can create stars or you can use glittery nail polish as stars. As a last step apply top coat to protect your design.
I hope you enjoyed!