Source: ACBL
One of the easiest things to do is counting, and curiously, it is not that hard to learn. But the world is not yet into this fascinating aspect of bridge.
With both sides vulnerable, South dealer, the West player holds 
A8 
AKJ876 
K63 
43.
South opens 1. Should West bid 1 or do you prefer a double, intending to bid hearts later?
This hand is short of doing that for two reasons. The first is that the hand is not quite good enough to double and then bid hearts. You need the Q as well as what you have. If the opponents can jack up the bidding you won’t be happy having to bid 3.
Also, because you have short spades, you won’t like it much if your partner insists on spades. West does bid 1 and East bids 1.
In your methods, is 1 forcing, invitational or weak?
The important thing is that you and your partner know what 1 means. I like to play that 1 shows a few points and welcomes further bidding but does not demand it. East could have from 6 to 11 points although he might bid 1 with a tad less if he had six or seven spades. South rebids clubs and West has another chance to bid. With East bidding 1, there must be a chance for game here.
3 shows the excellent suit and extra values. East may pass if he must, but he is being asked to go on. North finds a late voice in the bidding when he raises to 4. East and South pass and West has a final say in the auction. Pass, double and 4 are possible choices.
Do any of these calls appeal to you? As a rule, when you have been able to show your hand exactly, it is unwise to keep bidding. This hand has shown its six-card suit and sound overcall and East has passed, a strong expression. One thing West should worry about is finding East with a singleton heart.
West’s hearts are good but they are not so good that they can handle, say, Q-9—x—x in the North hand. You may, if you wish, double. You have four potential defensive tricks and you have a partner who did a little bidding.
West leads the A (ace from ace—king): 
East plays the 2 and South the 9. The queen is missing. Should West play the A, the K or something else? Best is a low heart.
If East has the queen, South is ruffing. If South has the queen, this play will get East in with a ruff and that will suit you, since it will have him on lead, not you. South ruffs East’s Q. It looks like your side might have had a heart contract after all. Do you think you missed 4? Not likely. East heard your bidding. If he started with the Q 2 and still chose not to raise, you can be sure he had a minimum 1 bid. After ruffing the heart, South plays the K and leads the J to dummy’s ace, East playing the 5 and 7.
Do you think East has another club? The odds are that he does not. South bid clubs twice, which suggests he had six. Further, East played the 5 and 7. If he had three clubs he could have played the 7 and 5, a high-low that would say he had an odd number of clubs.
Declarer’s bidding and your partner’s play suggest that South started with six clubs and your partner is out of clubs. Declarer leads dummy’s Q to East’s 4 and South’s 2 and your king.
What do you know and what do you do?
South opened 1 and rebid 2 all by himself. You know he had six good clubs and it is certain to have the A. That only adds up to 10 high-card points. South probably has some values in spades. Given that South has the A, you have to be aware that he will run the rest of the diamonds as soon as he gets in. He will get rid of as many losers as he can. You have one heart trick and one diamond trick and need two more. Can you tell what to do now with-out guessing?
Counters have no problem knowing what to do. Non-counters may be interested. If you admit that you have failed once in a while to count out a hand as declarer or as defender, stick with me. You will see just how easy this is. How many tricks does declarer have at this moment? Here is how to tell. Start counting them. South has six club tricks for sure. South has three diamond tricks for sure. He has no heart tricks which means he has only nine tricks that you know about. He cannot take 10 tricks unless he gets a trick in spades. If he has the K Q, he will get a spade trick, but if he has a lesser holding like K—x—x, he won’t get a spade trick unless West leads spades. Here is another way of looking at this. If South has three diamonds, then he has three spades, and that means that he still has two spades left after discarding a spade.
If South has two diamonds, then he has four spades, and that means that he still has two spades left after discarding two spades on the diamonds. No matter what South’s distribution is, he will always have two spades left after using all of his diamond tricks. West’s correct play is to lead any-thing back except a spade. Here is the layout: 
At the end, South led to the K and was down one. You can see that if West had led the A at any time, South would have had an easy road. For the record, a double by West would have worked, but only with good defense.