This is your trump suit and you are playing a slam.

ªK J 3 2

ªA 8 7 4

The obvious way to play is ªA and finesse ªJ.  That makes three tricks if the spades are 3-2 with East holding ªQ and four if West holds ªQ.

If spades are 4-1 that will make three tricks when West holds ªQ or if East holds ªQ singleton.

If you need four tricks you must finesse ªJ.  Playing ªA first merely saves you a trick if East has ªQ singleton but you still fail.

If you only need three tricks

Try leading a low spade from South.  If West plays ª9 or ª10 finesse ªJ otherwise play ªK.  You still make three tricks if they are 3-2 and East has ªQ and four if West has it.  But if West has ª9 or ª10 singleton you will make three tricks.  On the second trick West will show out and you can finesse East’s ª10 or ª9.  You also make three tricks when either player has ªQ singleton.

Just one word of warning.  Let’s say you follow this advice and West plays ª9 or ª10 and you lose to a singleton ªQ.  When you play ªK East, not West shows out.  If West is a tall gentleman say “Well played Andrew”, if he has a Swedish accent say “Well played Gunnar” and otherwise he is probably Tony Forrester.  If anyone else does that to you please let me know his (her) name.