The Gibson Les Paul Junior®, SG Junior®, and other single-pickup guitars have perhaps the least complex wiring setup of any electronic instrument.
Reduce unwanted electrical noise by using shielded coaxial cable for your longer wiring runs (for example, the connection between the controls and the output jack). Coaxial cable contains a center "hot" conductor which is shielded by an outer braid used for the ground wire.
For short connections between components, use standard non-shielded wire. Typically, white wire is used for hot and black for ground.
Stewart-MacDonald wiring kits contain black and white non-shielded wire, plus shielded coaxial cable. Extra black wire is included for running a string ground to the bridge.