What are the three basic rules of wiring?

The three basic rules of wiring: turn off the power and prove it dead with a tester, size the wire to the breaker protecting it, and make every splice inside an accessible junction box.

Each rule buys a specific safety. Verification catches the mislabeled breaker that kills people. Wire-to-breaker matching keeps conductors from cooking inside walls: 14 gauge to 15 amps, 12 to 20, 10 to 30. Boxed splices keep the inevitable loose joint from meeting insulation.

A worthy fourth: ground everything, and never lift a ground to make something convenient.

These are the floor, not the ceiling; the NEC adds several hundred pages of refinement on top.

Rule two is a lookup: the wire size and amp rating tool pairs every breaker with its conductor instantly.