Tip 1 -   Contract 6 § by South           (Degree of difficulty = 10)

West leads the Ace and the King of spades. How should South plan his play?

To take 12 tricks is sufficient that South ruffs 3 spades of dummy, reversing the hand.. To do so, since there are sufficient entries in dummy's hand, it is necessary that trumps in opps' hands are split 3-2, which happens to be in 67 % of times.
The contract is not sure, but there are not alternatives!
South should ruff the second round spades, play the ten of trumps for the 2 of dummy and then a club for the king at dummy.
Ruff the second spade in your hand and play 3 of hearts to the king of dummy; play now the last spade of dummy and ruff it with your last trump.
Return to dummy with the Ace of diamonds to play the 9 of trumps and to draw the last trump while you discard the loser heart. Now your hand is estabilished and you take the remaining tricks.

Tip 2 - Contract 6 © by South (Degree of difficulty = 5)

West leads the 3 of diamonds. How should South plan his play?

Planning: You could have 11 tricks, giving only the Ace of trumps.
You could take 3 hearts plus one ruff of a diamond in your hand, 4 spades, 2 diamonds (Ace and King) and the Ace of clubs.
It is obvious to look for the 12th trick at the finesse clubs. But you know that finesse works well on the 50% of time.
Then I ask you if there is a more likely play….. And the answer is affermative!
You may afford to ruff not one, but two diamonds in your hand since you have very good trumps!
After you ruffed the two diamonds, you proceed to draw trumps.

Tip 3 - Contract 4 ª by South (Degree of difficulty = 3)

North opened 1 clubs, South bidded 1 spades and West doubled. After the help 2 spades by North, South closed at 4 spades.
West leads the 4 tops of diamonds, East following the first round and then discarding 3 small hearts. How should South plan his play?

South should ruff the fourth round Diamond, cash only the Ace © and then ruff the 6 © with the Ace of trumps at dummy. Now he can draw trumps and claim the rest of the tricks.

Tip 4 - Contract 3 NT by South (Degree of difficulty = 3)

West leads the Queen of clubs. How should South plan his play?

South should duck the lead clubs and win the continuation in the suit in his own hand.
Now he plays a low diamond towards dummy's Queen before trying the heart break, that is a supplementary chance for the declarer that will not run away!
South maintains his job taking 2 spades, 3 hearts, 2 diamonds and 2 clubs.

Tip 5 - Contract 3 NT by South (Degree of difficulty = 5)

West leads the 6 of hearts. How should South plan his play?

South should  play a low card from dummy on the leading attack; doing do, he avoids squandering dummy's honour cards and ensures two stoppers in the suit. South covers whatever card East plays and then knocks out the Ace ¨.
East will no doubt continue hearts for their best, but declarer makes 4 diamonds, 2 hearts and 3 spades.
Remember this: Honours are not for squandering!

Tip 6 - Contract 4 ª by South (Degree of difficulty = 10)

West leads the 6 of spades. How should South plan his play?

If you look at losers in your own hand, you realize to have 4 losers. If there wouldn't have been the lead trump, you could ruff a loser heart with the Ace of trump, but with the lead trump ruffing at dummy is no longer possible.
When you give the hand to opps, they would play again trump, eliminating that possibility.
But, if you reverse the dummy, you could ruff in your own hand the loser clubs of dummy. So, here it is the winning prosecution: taken in the hand with the 8 ª, play the 2 § for the Ace and ruff a club, play now little hearts for the King and ruff again a club. Another little heart for the Ace and ruff your third clubs; go to dummy with the Ace of diamonds to ruff the last club with your last trump. You will make one spade on the lead, then 4 ruffs of clubs, the Ace of trump, the Ace and the King ©, the Ace  § for a total of ten tricks.