When to lead passively

The confidence of the opposing auction, the degree to which they pushed to their final contract or likely have values to spare, should be taken into account when leading. Contrast these two uncontested sequences:

What happened
West looked no further than the standard lead against notrumps, fourth highest of the longest and strongest. Declarer ran his ♦ 7 round to East’s ♦ 10 and ♦ J, then led ♠ 3 to ♠ Q. East won ♠ K and returned ♦ 4, West ducking the trick (to preserve communication to dummy’s ♦ K.
Declarer crossed to ♠ A, noting West’s ♠ 10, then led back ♠ 8. East won ♠ J and led ♦ 2, enabling West to score ♦ A and ♦ Q, all players discarding hearts. Declarer won West’s ♥ J switch with ♥ A, cashed the promoted ♠ 9, discarding ♣ 4, then led ♣ 3 to ♣ J. The finesse succeeding, he could score the last two tricks with ♣ AK. Nine tricks and game made.

What should have happened
The only two opening lead cards in West’s hand to let 3 NT make are ♦ 7 and ♦ 9. ♦ AQ97 is a very dangerous lead; it will work out fine in those minority of occasions where you find partner at home; but it is highly likely to give away a trick the rest of the time. Given the unconfident auction, West should have been unwilling to give up a cheap trick on lead. He should have opted for the passive ♥ J.
Declarer stands no chance on ♥ J lead. The normal line is to win ♥ K and lead to ♠ Q. East will win ♠ K and clear hearts. ♠ A and another spade will see East win ♠ J, cash the long heart, and West must come to ♦ A. Down one.

If you remember one thing...
Lead passively against an unconvincing auction.