-All high cards, jack through ace, in each suit are used.
-N/S can win all of the tricks except one in no-trump.
-N/S can not win all of the tricks except one in any suit.
In addition, minimize the N/S HCP.
Here's an example:
N/S has 5 top tricks.
In no trumps, cash ♦A and ♣A, discarding a heart. Now lead the ♦K pitching a spade. If west pitches a spade, play a heart to the ace and concede a heart. If west throws a heart, you have an extra heart winner.
If the end position is in any suit except diamonds, you have 2 unavoidable losers, and in diamonds, if you try the same squeeze east ruffs when you play a heart, or if you play ♦AKx, east returns a spade! and you have to lose a heart at the end.