Leads from a strong hand by Matthias Huberschwiller

A: ♠3 - Your partner has certainly nothing.
What is your only chance to beat this contract?
The spades! Therefore you need to lead the fourth best and hope to establish them.

Your result so far:

A: ♥J - You still have as many points as in question 1, but you only have four spades.
The chance of establishing a trick from length has become very small.
The best hope to beat the contract is to avoid giving away the ninth trick and hope that South does not find nine all by himself! Therefore you need to find a neutral lead, the ♥J.

Your result so far:

A: ♦Q- Your partner has nearly nothing, how do you think you could get him on lead to get a ruff? It will be impossible!
Therefore, you must not lead your singleton heart, which bears the risk to even help declarer, but from your sequence in diamonds, trying to establish a trick there.

Your result so far:

A: ♠6 - Partner, your lead! Well, unfortunately this is not possible, you'll need to chose a lead!
Leading your singleton trump can be bad if your partner holds Qxx, even if declarer could always decide to finesse because of your double.
But leading any of the other suits can be equally terrible because the points are in declarer's hand. As your partner has nothing, even a heart lead bears the risk of giving away a trick if N/S have the ace and queen.
In the end, it is the trump lead which is the least dangerous, hoping that all your points in the other suits will permit beating the contract later!

Your result so far:

A: ♥A - You look at your two possible tricks with pleasure (a trump and the ♥A), and happily lead the ♠J - and declarer discards his heart loser on dummy's spades!
Careful, against a slam, when you hold the setting trick in your hand, you need to lead an ace to avoid a discard!

Your result so far: