Here are three opening lead decisions I had to make in Day 1 of the North American Swiss Teams. Two worked out well, one didn't. On each one, if you get it right, they go down. If not, they make their game. Decide what you would lead in each of these before reading on. All involve a decision on whether to make an aggressive or passive lead.
1. You hold, in second seat:
RHO deals and opens 1NT, strong. LHO transfers with 2 Diamonds, then over 2 Hearts bids 3NT. RHO bids 4 Hearts, which ends the auction.
2. You hold, in 4th seat:
RHO opens 1NT after 2 passes. LHO bids 3NT.
3. You hold, in second seat:
RHO opens 1 Club. LHO bids 1 Diamond. RHO rebids 1NT. LHO bids 2C, alerted as a puppet to 2 Diamonds. After RHO bids 2 Diamonds, LHO now bids 3 Diamonds, and RHO bids 3NT. Before leading, you learn that LHO is inviting 3NT with a diamond suit. You also learn that RHO would bypass a 4-card major after 1C-1D, and that even after LHO's bid of 2 Clubs, RHO would not bid a 4-card major instead of accepting the puppet request.
An aggressive lead would be a spade, a passive lead a heart. I chose a low spade, which turned out successfully. Dummy came down with
Declarer played a low spade, won by Jenn's king. She played the ten of clubs. Declarer finessed, losing to my king. I now shifted to a diamond. Jenn had the KJ over dummy's queen as well as the ace of trumps, so we established a trick in each suit. We actually set it two tricks, since I was able to get a diamond ruff as well. Had I led a trump to start with, Jenn would have had to find the difficult defense of a spade shift from her king into the Ax in dummy. At the other table, a trump was led and they didn't find this defense, so we won 13 IMPs.
An aggressive lead would be a spade; a passive lead would be a club. I didn't think that I would be able to set up such a weak suit as J9xxx, so I thought the best shot was to find Jenn with a spade suit such as Jxxxx or Txxxx, with the opponents' spades 2-2, or possibly 4 to the Jack or ten with an opponent holding Tx or Jx, respectively. So I led the king of spades. This turned out to be wrong, since the opposition had only 8 tricks if I made a passive club lead, and the spade lead set up the ninth trick. Dummy held
Note that declarer cannot set up a ninth trick in a red suit. The spade lead allowed declarer to set up a second spade trick by winning the ace and playing back the jack. Now, after Jenn wins her ten, the dummy has an established spade winner for trick 9. My counterpart led a passive club, and we lost 12 IMPs.
It sounded to me like the opponents had a long diamond suit ready to run, so we might have to cash out our tricks right away, either in clubs, hearts or both. So, in order to retain control, I led the king of clubs. This catered to Jenn holding either good clubs or good enough hearts for me to get her in for heart plays through declarer. This worked out very well, as she held QJTxx of clubs and the heart queen! We cashed out the first 7 tricks for down three. In this case, a low club would also have succeeded, but anything else would have been a disaster, as the opposition had 6 diamonds and 3 spades ready to cash. This got us +300 and 10 IMPs, as our teammates played it in 3 Diamonds, making 3 for +110. If we had gotten this wrong, we would have lost 10 IMPs instead, a huge 20 IMP swing.