You decided to play the Spade King first, . Lets handle your questions.
Quote
1/. which hand should I be playing this from
Dummy, but.... don't play a spade... I assume opening lead was queen of diamonds. So you win the ACE, thus your next play will be from dummy.
Quote
2/. were there any clues as to what to expect
There are always some clues, did the opponents bid? What did they lead? What did they signal? None of these clues will be all that helpful on this hand. North passed as dealer, so you can eliminate hads that he would open 2D, 3D, 2H on (all weak)... But the usual inference that he doesn't have, say 6 or 7 diamonds is not so good because you can see the DIAMOND AK in dummy and west lead the queen (and presumably has the jack), so with six or seven diamonds to the ten at most, north would probalby not preempt anyway.
But a useful clue here is the lead. What did north play? A high diamond, a low diamond. Is his diamond play count or attitude. It is useful to know tihs as you construct the hand. If he played teh diamond 8, it could show a matching honor (in ths case the ten), or it could show count (even number if standard carding).
Quote
3/. what is best line of safety play
The way to make 6 is on bad (but not horrible) defense. That play is to win teh diamond ACE, KING (pitch a club), and ruff a diamond. All follow. Now club to the ace, and ruff a club (all follow, north plays the club king... did south go out of his way to give the count in clubs? Did south hesitatie a little before ducking club jack?) A heart to the ace and lead another club to ruff... here north has a problem. Does he ruff? The best play is to ruff with the spade 8 or 9, a heart instanty fatal (you make 12). But likely he will discard his last diamond.
Now you have a clue. Norrth looks like a man with 4D, 2C, and unwillingness to pitch a heart.Does that begin to paint a picture. You ruff, now a heart to dummy. This is the stituation after you win the second heart is dummy.
Sometimes if you don't know how to play trumps, not playing them at all works out ok.
Good defense willl hold you to one overtrick. Here, when you lead the last club form dummy North must ruff with the 9 or 8. If he discards his heart queen. You ruff. Cash spade ace, and exit a heart. He ruffs but has to lead into dummy's KJ.
Quote
3/. what is best line of safety play
Wel, the line I just gave is not very safe. You have 5 sure spades, 2D, 1C, and 2H if nothing gets ruff. So the safest play, is spade king and a spade. Playing around in other suits have risk of winner getting ruffed.