Opening Leads: When to lead trumps

On many hands, your choice of an opening lead involves using clues from the auction to decide whether you should make an aggressive lead, or play it safe with a passive lead. You'll have a slightly different type of decision to make when you consider 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 serves to shorten declarer's or dummy's trump holding. The types of auctions that will give you the strongest clues about this include those where:
(1) Declarer has shown a two-suited hand, especially if you have a good holding in declarer's other suit. Many good players consider it virtually mandatory to lead a trump to an auction like this one:
        West     East
         1D       1H 
         2C       2D      
         Pass
If you hold 10962 KQ6 83 AJ97, lead the diamond 3. It's a strong possibility that dummy will be relatively short in declarer's second suit (clubs), and you expect declarer may try to use dummy's diamonds to trump his club losers. Both opponents have shown minimum hands, so they may not have enough in high-card power alone to make their contract.
(2) You expect the short-trump hand (usually dummy) to be short in another suit. You can almost see dummy's singleton club after this auction:
        West     East
         1D       1H 
         1S       1NT      
         2H       4H
         Pass
Opener's sequence here typically shows some extra values with 3-card heart support. Since opener pulled partner out of 1NT, you expect that he has an unbalanced pattern -- probably 4-3-5-1 -- and that the opponents are in a 5-3 fit. If you hold:
109 975 QJ76 AK43 ,
resist the temptation to cash a high club, which may give declarer the tempo he needs to trump two club losers in dummy. You want to lead trumps as many times as possible, so start with the heart 5. If declarer wants to set up ruffs in dummy, he'll have to lead clubs himself, and you'll be in again for a second trump lead.
(3) You have a clear advantage in overall power. This may be especially important if you've doubled the contract. After an auction like:
        You      LHO    Partner   RHO
        1NT      Pass     2C      2S 
        Pass     Pass     DBL     All Pass
a trump lead is a good idea, even if you have an unattractive holding, such as:
Q92 QJ10 KQJ2 A103.
Although partner should have a fair spade holding, his double may have been partially based on his knowledge that the two of you hold significantly more than half the high-card strength. In this case, declarer's only prayer will be to score tricks with a few of dummy's trumps. Every trump lead you make may cost him a trick.
(4) You have a clear advantage in trump length and/or strength. In this auction:
        RHO      You     LHO     Partner    
        1D         DBL      All Pass
partner rates to have better trumps than declarer, so you'll want to attack declarer's holding. You may even be able to draw all of declarer's and dummy's trumps. This is one of the rare exceptions to the "rule" about never leading a singleton trump.
"Passive" trump leads

On some hands, you may be reduced to leading a trump just because nothing else looks safe. After a 1S-2S auction by your opponents, you have an unattractive choice of leads from:
754 A1072 KJ32 J4 .
All the unbid suits look dangerous, so try the spade 4. You don't necessarily expect this to hurt declarer, but you hope it won't help. Since partner has only one or two trumps, probably the worst that can happen is that you'll find his doubleton queen -- and that's something declarer may have found for himself anyway.
A few warnings: When in doubt, avoid leading a trump if you hold:

A singleton trump. Your shortness suggests partner has length, and this lead will often pick up any honors he might have. It's better to lead a long suit and try to force declarer to trump himself down to the same or shorter length than your partner.

A "dangerous" honor holding like Jxx, Jx, K10x, A10x or Ax. These will be safe only if partner holds no honors in the trump suit. If he has the jack or queen, a lead from one of these combinations can make one of your natural trump tricks disappear immediately. Or, more likely, it will give declarer a finessing position that will let him pick up the suit on the next lead.

For tips on strategies to use when making non-trump leads, see:
Aggressive Opening Leads
Passive Opening Leads

　