A nice little nugget that I learned initially from a friend and partner, Kenny Eichenbaum:
"A minimum signoff says that your answer to RKCB would be worse than Two-with-the-Queen."
This is a relatively simple rule to use, and it may be of interest to many. A simple example might be a Jacoby 2NT call, Opener jumping to 4H to show a minimum. But, what precisely is a "minimum?"
A hand where you have "Two-without-the-Queen" might not be a minimum, of course. You might have serious extras in the form of Kings and Queens in side suit, or great shape, or both. However, the definition, if you will, of a "minimum" is "a weak hand, but not two with the Queen or three+ key cards."
This is a helpful guideline in many sequences. A recent BBO forum question shows the value. Responder, after partner opened One Heart, held KQxx-xxx-KQx-AKx. Some bidding styles involved Opener jumping to 4H to show "a minimum." But, what "minimum?" Would AJx-AKJxx-xxx-xx be a minimum? That's only 13 HCP's, but slam is really close. How about Axx-AKQxx-xx-xxx? That's 13 also, and slam looks even better.
In the actual situation, many Responders decided to bid 4NT, ending at 5S when Opener turned up not having one of the two missing side Aces and only holding KJxxx in trumps, making the five-level very precarious. Had this rule been in place, Responder would know that Opener's response was going to be 5H at best and would never have even asked the question.
In the actual situation presented on the BBO forum, my techniques would have made this rule unnecessary, as the heart problem and lack of a spade Ace would have been revealed through a normal cuebidding sequence. However, this rule does have a place, such as when Opener is balanced and hears a Jacoby 2NT call from Responder, or when a major is agreed after a complicated or contested sequence.
BTW, Kenny is apparently in the process of re-writing "Bridge Without a Partner." The original version took some heat for a number of reasons, but the stories were incredibly hilarious and all real. His goal this time, among other things and in addition to including some new tales, is to have a kinder, gentler treatment of the intriguing "partner." I look forward to this new version, for a good laugh at ourselves.