When the dummy goes down, take time to look at it.

If playing in a suit - what cards are missing?

What tricks are you going to lose?

Lead is Ace of Clubs.

Pull trump.

You can get 5 Spades, 2 Hearts, 1Diamond and 2 Clubs to make the contract.

South opens 1 Club

North responds 1 Heart.

East bids 1 Spade

South 2 Clubs and North goes to 3 NT with a stopper in Spades.

East leads the A of Spades.  Why not 4th down?  When North bid NT he is showing a stopper in Spades so take the Ace.  You may not get back in to play the Spades.

Play the Clubs forcing the opponents to dump cards.

Once the opponents take their two Hearts North has the rest of the tricks, making 4.  The 10 and 9 are now good and you have transportation.

Depending on your bidding style 4 Spades may be played by North or South.  

Final Bid 4 spades South

Lead K of Hearts.

With 9 Spades play for the Queen to drop on the A, K.

If played carefully South will get 5 Spades, 1 Heart, 3 Diamonds and can "ruff" a club.

Final bid is 4 Hearts in the South.  EW have bid Diamonds.

Lead A of Diamonds.

South trumps the next Diamond and leads a 10 of Hearts.  Bad news!  Hearts split 4 - 0

Knowing what Hearts are missing is the answer to this problem.  The A, J, 3, 2 are on the right of the Declarer.  Play the King on the boards, forcing the Ace.  Now the three outstanding Hearts are all below the Queen in the Declarer hand.

Go to the board with the Spades.

Play a heart.  If they play the Jack, take it with the Queen.  If the duck, play low in your hand and lead again from the board.  If they duck again come back to your hand with a Spade and pull the last trump.  Easy?  Makes 4.

The important thing is knowing what Trump are missing.  You know where they are.