The Lead's The Thing

As declarer, the clue that helps me figure out the hand the most is the opening lead. There is a wealth of reliable information available from it, especially when the opponents lead count (which is very common in North America). People rarely falsecard the lead because it is also the card that helps their partner figure out the hand the most, and presumably are trying to make the most effective lead possible. There are many leads that "everyone" makes, so when they don't you can take negative inferences as well. Here are a few common inferences to take that many people fail to think about:

Playing NT

• When the opponents lead from a 4 card suit, they will not have a 5 card unbid suit. The reason is simple; people generally lead from their longest unbid suit. There are a few exceptions, the most obvious being if they led from a sequence like KQJT. This inference, especially if there are no unbid suits, can help you guess the distribution very accurately.
• When an opponent leads from xxx, he is trying to make a passive lead. This generally means all of his other leads are "unsafe" and he will usually have honors in every suit. If you have to guess a side queen for instance, definitely finesse through this player. If you have bid 1 or more suits he probably has length in those suits.
• When an opponent leads from xx against an auction like 1N-3N then one of two things is happening. He either has nothing and is trying to hit his partner, or he has everything and is trying to be safe. You should be able to figure this out very early on.
• Many opponents will tend to lead majors on an auction like 1N-3N. If an opponent leads a 4 card minor against this auction, it's likely that he does not have a 4 card major.
• If an opponent leads Ace from what later turns out to be AKxxx(x), he thinks he has a side entry. If he leads low, he does not think he has a sure side entry. If you need to guess how to play the hand this inference can be useful.

Playing Suits

• If a player leads a stiff, he does not have a trump holding like Qxx, JTxx or Kx. Qx is unlikely. If you have to guess the queen of trumps after they led a stiff, hook through their partner.
• If you are off AK in a side suit and opening leader led a different suit, he does not have both the ace and the king. This can help you count the high cards in many cases.
• There are some auctions where a trump lead is automatic. For instance after a 2 diamond opener showing a 3 suiter with short diamonds and then a jump to 4 hearts people will almost always lead a trump. If they do not, they have some kind of vulnerable trump holding. This is true on all "auto trump lead" auctions.
• If a player leads an ace against a slam, he thinks he has another trick. This inference is much stronger at imps than MP (where they may be trying to hold you to 6). Tempo is an important factor here too, the quicker the ace lead the more likely the opponent is to have a side trick like the trump queen.
• If a player underleads an ace against a partscore or game, they had no other attractive lead. Play accordingly.
• If a player leads a trump when declarer has shown a second suit, opening leader probably holds a strong holding in that suit.
• A trump lead is often an attempt to be passive with honors in every other suit.
• If a player underleads an AK(QJ) at trick 1, they have a void and are trying to get partner to get in to give them a ruff.

I think you get the idea. Here are two example hands to help illustrate some of these clues.

Hand 1

A52
843
AJT2
J76

K83
K97
K984
AK4

You are in 3N on the auction 1N p 3N. You get the 2 of hearts lead to the Q and King. The opponents play 4th best. How do you tackle diamonds?

LHO has 4 hearts and RHO has 3. The rule of empty spaces makes RHO a 10:9 favorite to hold the queen of diamonds. However, there is a stronger clue. Remember that we are going to assume LHO has no other 5 card suit since he led from a 4 card suit. His possible shapes are 4423, 4432, 4441, 4414, 3433, 3442, 3424, 2443, 2434, 1444. With other 4 card suits, especially spades, he may have led that instead. It also appears he led from an unattractive holding like AJxx, but RHO could have AQx of hearts still. Overall 3433 is his most likely shape, but even if all shapes are equal there are 7 shapes where he has 3+ diamonds and only 3 where he has 1 or 2 diamonds. This makes finessing through LHO a strong favorite despite the rule of empty spaces.

Hand 2

K42
KJT3
A532
87

AJ983
Q9762
64
3

This comes from a national team game. The bidding may scare you, but north opened 1, south bid 1, north bid 2, and south jumped to 4. West thought for a long time and led a low heart. I put in the jack and RHO immediately played low. How do you play?

Clearly, LHO had underled his ace of hearts. He must have had a terrible hand to lead from because that is a very strange lead and not the slightest bit attractive. I decided that my LHO must have the queen of trumps. Accordingly, I won the queen of hearts in my hand and advanced the jack of spades. LHO shrugged and covered so I did not think he had QT doubleton and finessed the spade ten on the way back. LHO did have the Q6 of spades.

That was a spectacular hand, but not a very hard play to come up with if you are in tune with the vast information available from the opening lead.