These series of article were written by Eric Kokish and his wife Beverly Kraft.
After a simple auction – 1NT-Pass; 3NT-End, your partner leads the 
6. Which card should you play with each of the following holdings, and why?
Case 1: Dummy has Q 2, and declarer plays the queen.
a) J 10 3
b) J 9 7
c) 10 9 4
d) 10 8 3
e) 9 3
When you cannot cover dummy’s honour partner may be interested in either of two pieces of information: (1) how many cards do you have in the suit led, or (2) whether you hold a complementary honour (in this case the jack). You cannot answer both questions with a single card so you must agree with your partner on one message or the other. When dummy’s honour is unsupported (as here), it is more common to signal information about the complementary honour – option (2).
a) Play the jack, which usually shows the 10 but might be the winning play from jack-small to unblock the suit. Picture partner with ace-ten-sixth, declarer with king-third.
b) Play the nine, encouraging; this suggests that you hold the important card card below dummy’s honour – the jack.
c) Play the 10, which shows the nine but denies the jack (signal with the highest of equal cards). This might help partner if he holds KJxx.
d) Play the three, discouraging. Partner is looking for the jack, not the ten.
e) Play the three, discouraging. Partner cannot tell how many you have (this is not a count situation) but he’ll know that you cannot help him develop the suit.
Case 2: Same auction. Dummy has the Q J 2, and declarer calls for the queen.
f) 9 8 5
g) 10 5
h) 10 8 4 3
i) 10 8 7 5 3
This time partner’s only interest will lie in the number of spades you hold. He will want to know whether it is safe to continue the suit (when he has led from $K10764, for example) or whether your side has a future in the suit (when he has led from A10764, for example); he will lead a second low spade in both these cases when he believes you have three spades, but not when you have only two.
f) Play the five, low from an odd number reveals your count accurately.
g) Play the 10, highest from an even number reveals the count
h) Play the eight; it is standard practice to play second highest from four; with this agreement in place, partner would read the four as a doubleton or low from three, but never from four (the deuce in dummy precludes [say]8432).
i)Play the three, low from an odd number, as in (f). Here, however, you have five, a surprise. Partner seems to have found an inspired lead from ace-third or king-third. With the latter holding, it may not be possible to unblock the suit in time. Nice lead, partner, just the same.