Rule of One
When drawing trumps, if Defenders hold one last master trump
Don't draw it!
It will take two of your trumps for a trick that will win.
Make them ruff another suit.
Rule of Two
Lead top of a (remaining) doubleton
When defending and you have only two cards left in the suit, play the higher
Rule of Six
Rule of Seven
When holding just one stopper in the suit led (in Notrumps), add up the number of cards in your hand to dummy's. Subtracting the total from seven will tell you how many times to duck.
Rule of Eight
Use after a No Trump opening
You need 6 or more points
Count your losers
Deduct losers from the combined length of your two longest suits
If result is 2 or more make an overcall otherwise defend.
Rule of Eleven
If the lead is 4th from top (an honour)
Deduct the face value of the lead card from 11
The result is the number of cards higher than the lead card held in the other three hands
Rule of Fourteen
You may respond in a new suit at the two-level when your HCP + the number of cards in your suit equals fourteen or more.
If not - but with six + points - respond 1 NT.
Rule of Fifteen
In the fourth seat after three passes -
If you too have less than an openoing hand you should open the bidding if the number of high card points and the number of cards in your ♠ suit equals fifteen.
Otherwise the opposition may find a fit in their suit by overcalling.
Rule of Twenty
Open the bidding when your total points added to the number of cards in your two longest suits equal twenty or more.
The hand opposite has 11 HCP plus 5 cards in ♠ and 4 in ♦ so open the bidding.