So, our partner has opened with a pre-emptive bid at the 3 level. This tells us they have between 5 and 10 points and at least 7 cards in the suit.
Let's start by looking at this hand where our partner has opened with 3
Unsurpisingly, we have very few Diamonds, and unfortunately only 6 points, so in this instance we will PASS. Let's generate a rule for this.
If less than 12 points AND less than 3 cards in the supporting suit, PASS.
So, what about this next hand. Partner has again opened with 3
Our hand is showing only 5 points, but we do have 3 Diamonds in it. With our partners Diamonds too, we are likely to be holding most of them, so let's raise the bid to 3NT.
If you have 3 or more of your partners bid suit raise to 3NT.
And what about this hand, Partner has again opened with 3
Alas, only 1 Diamond in our hand, but we have a load of points. This, along with our partners tally, again hints to a 3NT response.
If you have 12 or more points, raise to 3NT.
In fact, we can merge those two rules into one.
If you have 3 or more of your partners bid suit OR have 12 of more points, raise to 3NT.
Ah, but hold on...we're forgetting that about our minor and major Preferred Suits. 3NT works fine for Diamonds and Clubs, but if our partner had opened with say 3 or 3 then it would be better to jump to 4 of the suit, so let's amend the rule slightly.
If a Minor suit and you have 3 or more of your partners bid suit OR have 12 of more points, raise to 3NT.
If a Major suit and you have 3 or more of your partners bid suit OR have 12 of more points, raise to 4 of the suit.