It's not a simple concept, but:
1) Twisting pairs of signal wires reduces EMI (Electro Magnetic Interference)
2) Shielding a wire or enclosure (surrounding in metal) reduces RFI (Radio interference)
3) The shield and the ground should be connected at one end only.
4) Since this is somewhat audio related, transmitting a signal on a balanced input (usually XLR connectors) tends to eliminate "ground loops".
5) A ground loop is where there are multiple grounds and a potential builds up between them, this causes a large current through a small resistance and bad things start to happen.
6) Crossing wires is better than running say a signal conductor in parallel and next to a current carrying conductor.
7) Signal grounds (analog ground, Digital ground), power ground and protective ground need to all stay separate and then connected at one point which is the reference.
8) Your house should references all the plumbing, electrical, telephone and cable to a a single earth point. If an internal line gets hit by lightning, then that large current travels direct to Earth and thus other circuits are not affected by the difference in potential created by the current. Their reference is still the ground.
9) Ground can vary over the distance of the earth especially when thunderstorms are in the area.