Fuente: ANDREW’S TIP: With trump length, lead length.
There are two diametrically opposite defensive strategies against trump contracts. You can lead from shortage and try to make your trumps by trumping; alternatively you can lead from length and try to force declarer to shorten his trumps so you gain trump superiority.
With four (or more) trumps you should generally lead from length and try to force declarer – this week’s hand is a typical example:
West correctly led 
4 to East’s Q and declarer’s A. At trick two declarer led 
3 to dummy’s Q and continued with K. West took his A and played a second . Declarer trumped and realised that if he drew all West’s trumps he would have none left himself. He correctly played 
5 to dummy’s K and East’s A. East played his third and declarer reluctantly trumped. He played a second and West trumped and played a fourth . Declarer trumped in hand with his last trump. Unable to reach dummy to draw West’s last trump, declarer played a third . West trumped to defeat the contract.
Note that if West had led 7 rather than 4, declarer would make 4 easily; East would win A, lead a second for West to trump, but he would only score his A in addition.
ANDREW’S TIP: With trump length, lead length.