We looked at the types of auctions that provide clues about whether to make a passive or aggressive opening lead. You have a different type of decision when considering a trump lead, which, depending on the auction and your hand, may be an aggressive or a passive choice.
Aggressive trump leads
On some hands, a trump lead can actually be your strongest attack because it shortens declarer’s or dummy’s trump length. The types of auctions that will give you the strongest clues about this possibility include those where:
Declarer has shown a two-suited hand, especially if you have strength in declarer’s non-trump suit. Many players consider it virtually mandatory to lead a trump to an auction such as:
West East
1D
1H 2C
2D Pass
If you’re South holding 
1098 
KQJ 
643 
AJ96 , lead the diamond 3. There’s a strong possibility that dummy will be relatively short in declarer’s second suit (clubs), and you expect declarer will try to use dummy’s diamonds to trump his club losers. Both opponents have shown minimum values, so they may not have enough in high-card power alone to make their contract.
A trump lead can also be an effective attack in other situations where the weaker hand shows limited trump support. These include auctions where responder takes a preference after opener makes a two-suited bid (Flannery 2D, for example) or a three-suited bid (Roman 2D opener). The same principle applies to two-suited overcalls: