Summary

First, keep things as simple as you can
Remembering that complexity isn't inherently bad

Clearly understand (and document) the potential for amplification to occur
Look closely at aggregated and mesh structures in your network
And remember that as things scale up, what was small can become very large

Clearly understand (and document) the where coupling occurs in your design and implementation
Localize the impact of any design or configuration change
Can also occur in operational procedures
Engineer for Human Entropy