Source: http://www.andrewrobson.co.uk
Some 25 years ago I wrote a Bols Bridge Tip. If a preemptor leads his suit, he probably has a singleton trump. The reasoning is simple: 7321 is (by far) the most likely shape for a preemptor; he’ll probably lead his singleton…unless it’s in trumps. [I won second prize].
On today’s deal from a duplicate at ARBC (Andrew Robson Bridge Club), West led the ace of clubs v 6
. Now West leading a club, when dummy’s leap to 6 (rather than, say Blackwood) strongly suggested a void club, implied that West held a 7 
(32)1 shape. With a singleton spade or diamond, might he not have chosen that card to lead?
- Heavy – and might chance a gambling 3 NT (showing a long, solid minor and little outside) at other vulnerabilities. Vulnerable, with a hole in clubs, 3 is prudent.
- Five-five in the majors, an extension of the Michaels convention. North needn’t be nearly as good as he is here, mind:
KQxxx AQJxx 
xx x would be fine. - Should have a good play if partner holds either red-suit king.
So ruff the club and play just one round of trumps (that’s the key), say the ace. Then play out the four top spades (revealing the 5-2 split), discarding three diamonds from hand as West can only discard on the third and fourth rounds. Ruff the fifth spade, then lead your remaining diamond to the ace and ruff a diamond (with the king).
We have reached this ending:
You now ruff a club with the jack of hearts. What can East do? If he throws the king of diamonds, you lead the promoted queen of diamonds. East ruffs perforce, but must lead from 108 round to dummy’s Q9. If East underruffs the jack of hearts, you again exit with the queen of diamonds, East winning the king and being similarly trump-endplayed. 12 tricks and slam made.
Note that if declarer had led to his king of hearts at trick two, preserving dummy’s AQJ, he’d have avoided the need for any trump endplay. Less fun though.