Any time a lighting instrument will be rigged or "flown" over the heads of human beings, properly secure it in a fail-safe manner. Tie off all instruments to a sturdy rigging pipe with the use of 1/8 inch aircraft cable with a fail-proof closure, clip, or carabineer. Double-cable very heavy instruments, like jumbo ellipsoidals. Turn off all dimmer circuits while connecting instruments for the first time.
If the theater is equipped with light bars, or "electrics" that can be flown in and out with a counter weight fly system, don't overload these electrics with too many instruments. Always have enough pig iron is loaded onto the counterweight system to balance the load. If you load a lot of pigs on an electric don't forget to remove excess pigs as the instruments are removed at strike. You'll create an imbalance in the system that could result in a fatal accident if the too-heavy pig iron mule comes crashing down on someone working with the system. Instead, remove pig irons incrementally as instruments are removed. If the counterweight ropes "sag" oddly when the unit is locked down, there is a problem with the weight balance: correct it. If the electric pipe seems to slowly drift down after being flown and locked into position, there is too much weight on the bar. Correct it immediately. Don't trust the system to work otherwise.
Lighting is no place to improvise hardware or rigging approaches. Check that each instrument has its proper cables, connectors, yokes and hanging c-clamps. Rigging "something for now" with odd wires, ropes, or gaffer's tape is never acceptable.
Don't gaff tape cables to the electrics or pipes. Black cotton stage twine is the only suitable material for securing cables to pipes. On a fly system, bundle cables together as they come down from the end of the pipe to avoid snagging any stray cables on drape legs and other dressings.
Schedule as much as eight hours or more for the proper hanging and focusing of lighting instruments. A good technical director will simply not allow a stage director to compress this critical task into a mere "hour or two" just before a rehearsal. Proper rigging takes time, and many skilled and patient hands, to get the job done in a safe manner.
Have a trained Technical Director or Master Electrician on hand to conduct the supervision of any rigging. Don't permit amateurs, and students especially, to install lighting instruments without this expert guidance. Sloppy rigging can claim lives.