Source: [ilink url=”http://www.acbl.org/”]2005 ACBL Bulletins[/ilink]
Aggresive or Passive?
When capable defenders choose a lead, they review the bidding, visualizes the dummy and tries to anticipate the play. They must always consider whether to lead agressively from honors, hoping to cash or establish fast tricks, or to lead
passively to avoid helping declarer.
West showed a good hand with a diamond suit, which may be strong since he took the trouble to show it and heart support. Lead a low spade, hoping to strike gold in spades before declarer draws trumps and establishes the diamonds for discards.
A spade lead is necessary to hold declarer to 10 tricks.
Since you have good hearts, dummy’s side suit is less of a threat. Moreover. East- West had a tentative auction to game and will have no extra length. Hence an aggressive lead, such as a diamond, isn’t needed. Lead the passive 
J.
The defense is entitled to a club and a diamond, but if South errs by leading a diamond, they must be careful, lest declarer make six. North must shift to a heart when he wins a club trick, else declarer will squeeze South in the red suits.
West rejected East ‘s effort to play at notrump, hence West has a shapely hand and likely a singleton diamond. Since dummy’s hearts are a threat, especially when you hold K-7-3, you must get busy, but a diamood lead won’t produce more than one winner. Lead a club from your strength, hoping North has help.
A club lead wins two clubs, a heart and a diamond for the defenders.
When your opponents stop at 2NT on this auction, they have no extra strength, and declarer must struggle, especially if his key suits don’t break well. You have the hearts tied up, and North is marked with at least four spades. Avoid an aggressive lead, therefore, that may give away a vital trick. If you defend passively, the contract may die of natural causes when declarer run out of tricks. Lead the 
9.
A spade lead beats 2NT. (So also does a low club to North and a diamond shift.)