I got this great, simple tip the other day.
Take any tape; masking, packing, whatever. Put a strip on the back of the object long enough to cover the holes, and poke through the holes in the tape with a pencil or something. Peel off the tape, and transfer the tape to the wall. If it's a painted wall or wallpaper, and you are worried about the paint, stick the tape to the carpet until it gathers enough lint to be much less sticky. Put the tape on the wall where you want it, drill the holes or put in the screws, and attach your object.
Pretty good idea, huh?