Track Bus : I use 2.5mm dia. Earth wire. Seen here on a recent layout extension. The first two wires are DCC (red) DCC (black) the other two wires are used for lighting signals and turnout control. ALWAYS stick to this convention when wiring. Keep it simple and only use Red and Black droppers for DCC connections, that way its easy to check wiring.

For DCC installations get some decent tools to abuse !

When tackling split frame chassis use two craft knives to collect the spring circlip that holds the motion in place.
Good lighting, and a clean work surface are essential.

For fitting smoke units into Chimneys a taper reamer is essential.

Get a loystoys decoder tester it can save you a lot of time and effort. It can also program static decoders.

When fitting plugs to decoders this is the convention

Save any off cut decoder wire from installations, it comes in very handy. Decoder wire can be obtained from LoysToys.