1. Separate power and signal
Run them in separate conduits with at least 100 mm between them, and cross at 90 degrees if they must cross. A signal cable running parallel to a mains cable for three metres will pick up hum that shows as slow horizontal bars.
2. Leave a service loop at every panel
300 mm of slack, coiled and tied, not cut to exact length. Panels get removed and re-hung; a cable cut to the millimetre will not survive the first service.
3. Label both ends before pulling
Not after. The label at the far end is the one that saves an hour, and it is the one people skip because the near end is right there.
4. Do not use cable ties on signal cables
Ties compress the dielectric and change the impedance. Use hook-and-loop. It also makes re-routing possible without cutting.
5. Keep cables off the back of the modules
A cable pressing on the rear of an LED module shows up as a faint pressure mark on the image within a year. Route along the frame members, not across the module face.
6. Allow for heat
Cables rated 70 degrees in a cavity that reaches 55 are near their limit. Use 90-degree rated cable in enclosed cavities, or ventilate the cavity.
7. Document the as-built route
Photograph the cable route before the panels go on. In three years when someone needs to add a signal, the photo is worth more than the drawing.
8. Plan for one spare pair
Pull one spare Cat6 and one spare fibre from the rack to the wall. It costs almost nothing during install and saves a re-cable later.
9. Earth the shield at one end only
For shielded cable, bonding both ends creates a ground loop. One end, at the source, is the standard. This single detail fixes a surprising number of interference complaints.