Minimum :

Enough alternator power (upgrades are cheap even if your engine doesnt have one with enough)
Correct wiring : One relay per fan
Temperature control
Fused connection feeding power to the relays
Shroud properly installed

Bonus points:

Triple relay setup on dual fans, high/low control
Using oem relay sockets and unused locations in the stock relay/fuse centers to install these, making the installation nearly invisible.

Nice stuff if you have a newer swap:

LS1 and LT1 pcm's do speed based fan control, cuts off the fans after a certain speed is acheived. Aside from coming standard setup for high/low instead of on/off.

The comments about your "relay mod" , werent about not knowing the terminology, I couldnt care what you called it, I knew what you meant, the issue was that you seem to list it as optional, and its far from it.