Why do we lead 4th down, particularly when we have a holding like AK982?
Doesn't it seem more reasonable to take the Ace and King and get that suit
set up right away?
Consider this holding:
DUMMY
T56
YOU PARTNER
AK982 73
QJ4
DECLARER
If you play the A, then K, and a small one, declarer wins with the Queen.   Although
your suit is now set up, if Declarer finesses into Partner, (avoiding the 'dangerous 
opponent',  when partner gets in, he can't reach your spades since he has none
to lead back.
Consider if you lead the 8 (fourth down).   Declarer gets the same trick, but if partner
gets in later, he can return your suit and it runs!
Last week we learned some standard leads  against no trump - (see calendar for lesson)
 - Top of a Sequence - 
 - 4th best from your longest - 
 - top of 2 touching honors from 3 card holding 
 - low from 3 card suit headed by an honor 
 - top of nothing
There's a few more leads to learn to add to your repetory of expert no trump defense!
INTERIOR SEQUENCE LEADS
KJT93 AJT83 KJT54 AJT6
With any KJT or AJT sequence, always lead the Jack.   This can be confusing since
the Jack would be lead from JT9 or JT8.   Just keep in mind when your partner leads
the Jack, he could concievably have the Ace or the King in that suit.  
Could he have the Queen if he leads the Jack?  (no)   Why?   (because he would lead 
the higher of 2 touching honors.  From AQJx he would lead the Queen).  Playing 
standard leads against no trump, leading the Jack denies the Queen (but may not 
deny the Ace or King.
Likewise from AT9, KT9 and QT9, with or without extended length, lead the Ten.
If your interior sequence begins with a 9 or less (A9842 or K984 or Q9842 lead 4th
best).  
IN ORDER TO LEAD AN INTERIOR SEQUENCE, THE SEQUENCE MUST BE 
HEADED BY AT LEAST ONE HONOR! 
Tens are honors - nines are not considered honors for interior sequence leads.
Finally, lets talk about a special lead against No Trump - that is the lead of the ACE.
The lead of the ace tells partner to 'throw down your honor'.  Whaaaat? 
Doesn't that sound kind of naughty?
The lead of the Ace against no trump in an unbid suit (your partner or opponents have 
not bid the suit ) guarantees the 4 top honors in the suit and is asking partner to unblock.
It is a command!   
AKJXXX AKJT AKQT AQJT
When holding Q64, J732, K83, throw down the honor. (It only hurts for a little while)
DUMMY
865
YOU PARTNER
AKJT Q3
9742
DECLARER
If you don't play the Queen under the King, Partner will think declarer has the queen
and will switch suits trying to get you in, so you can lead the suit through declarer
to get his queen.
What does unblock mean?  Take declarer's 2 and give it to partner.  If You lead the A,
then the King, then the Jack, partners has to play the Queen and now partner can't
lead the suit to make your Ten good!  Partner must drop the Queen under your Ace
and you will maintain the lead to run your 4 good cards.
LETS PUT WHAT WE LEARNED TO WORK!   CONSIDER THE FOLLOWING 
AUCTIONS AND WHAT YOU KNOW ABOUT LEADS.
Your hand:
KJ75 QJ96 76 JT4
The bidding has gone:
South West North East
1 NT pass 3 NT pass
pass pass Your lead? answer
Or like this:
South West North East
1 S pass 2 H pass
2 NT pass 3 NT pass
pass pass Your lead? answer
Or like this:
South West North East
1 S pass 2 C 2 D Your lead? answer
2 NT pass 3 NT pass
pass pass
What do you lead from the following holdings assuming the bidding was 1 NT pass 3 NT?
1) AKJT 97532 42 ♣87 answer
2) QJT6 K8653 52 ♣J7 answer
3) 863 Q842 K5 ♣QT42 answer
4) J86 KT932 J76 ♣K6 answer
5) 7 J9876 AT76 ♣Q32 answer