A fine line often separates a dynamic red team from a prescripted and predictable red team. Note that the following principles apply not only to red teaming, but to wargames, exercises, and studies in general.
I like these two:
Relevance; A good red team eschews ivory-tower pretension, addresses timely issues in a timely manner, yields practical insights, and does so in a way that connects these insights to real-world practitioners.
Discretion: “Don’t give good ideas to the bad guys.”