This is a simple hand, but it illustrates very important principles.

We have eleven top tricks plus potential in clubs. The key is in what we do with those clubs. We have two losers in the red suits. If we play those losers on ♣K and ♣Q, then we will lose one of those tricks but win the other. We will thus lose only one trick and make the twelve required for our contract. We will need two entries to dummy after trumps are drawn: one so that we can lead the ♣K, and one so that we can reach the ♣Q that we will have set up. So we should prefer to take the opening trick in hand to preserve ♦A until trumps have been drawn. We should also be mindful to play ♠J on the first trump round in case of a 4-0 split. The plan is to win trick one with ♦K, lead low to ♠J, continue with trumps until they are drawn, lead a heart to the king, and then lead ♣K and discard one of our red suit losers. West might win with ♣A, but when we regain the lead we have the ♦A as an entry to play ♣Q and discard our other red suit loser.

Discarding on the ♣K is called loser-on-loser play. The object is to discard one loser and set up a winner to discard another loser. Mostly we have just one high card winner to force out. That requires two entries.

Quite often we will have an immediate (quick) loser and an eventual (slow) loser. It is imperative to discard the immediate loser first. With the above plan of play we maintained two slow losers by using ♥K as our first entry to dummy. In general it is good practice to maintain a guard in each suit. We could have used ♦A as our first entry, but then we would have a quick loser in diamonds. We would still make our contract as long as we discard the quick diamond loser first. If we fail to do that, then the defence will win ♣A and take a diamond trick.

A mistake that many beginners will make is to lead ♣K, and when it is not covered, to ruff it. That does not achieve anything. The trump trick would always be made anyway, and nothing gets set up. We would still be left with two red suit losers.

You might be asking what we would do if we lead ♣K and East covers it. The answer is that on this deal, it doesn't matter whether we ruff it or discard. We can only set up one winner in dummy and we have two clear losers to dispose of, so ruffing doesn't help. But it doesn't hurt either.