h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Most institutional buildings and residential addresses have lighting outside, be it street lamps or private halogen searchlights. As no-one normally draws the curtains in offices or rooms where they are not sleeping or spending time after dark, buildings at light are often surprisingly well-lit. Greys are a better colour to wear here, as opposed to dark greens or blues, as you will blend in more with the drab, monochrome background.
On the subject of torches: despite what I just said, you often need more light to read or find things than you have, so carry a small torch. It should be small enough to fit in a pocket, preferably with an adjustable size beam, and not so bright so that the glare bouncing off paper and whitewashed walls will a) blind you or b) be reflected outside the room. Unless it is absolutely necessary, do NOT draw curtains or blinds. Often this will make a lot of noise, and this is the last thing you need, and normally it should be darker inside the room than out, meaning that the windows just become mirrors for those outside. Just try not to shine your light, if you have it on, near or at the windows, or in the general directions of the windows altoghether. Drawn blinds in an abandoned office look a lot more suspicious from outside than an empty window. "Trust me, I'm a professional." If you have any more questions, just ask!