There is a lot of discussion dedicated to which card should be led on the first trick. In general, the answer depends on factors such as what cards are held (both the length and texture of each suit), the final contract, how the auction went (fast or slow, confident or doubtful, information about opponents' and partner's suits), partnership agreements, and opponents' playing styles.
In discussing opening leads, it is useful to make the first distinction between defense against notrump contracts and against suit contracts.
Opening leads against notrump[]
The most common wisdom in leading against notrump is to lead the "fourth down from the longest and strongest suit". This is sometimes correct but is not true universally. In particular, the longest suit is not always the best suit to lead. The most important consideration now is what information was gained from the auction.
For fast auctions[]
In the case of 1NT-3NT or 1NT-2NT-3NT, where there is no suit information available, the opening lead must depend entirely on the cards held by the left-hand defender. In this case, suit texture is typically the determining factor, since it is a good predictor of whether a given lead will give up a trick unnecessarily.
- Suits with 3-card or longer sequences of honors are to be preferred for the lead, since the cards in sequence are effectively identical. This suit is nearly always the best choice, and in this case, the top card from the sequence should be led.
- For example, AKQ2, KQJT, QJT6, JT9: all these are good sequences to lead from.
- Suits with tenaces and gaps between the values are unwise leads unless there are 5 or more cards in the suit, in which case it pays to establish the suit anyway by leading fourth down.
- AQT, KJ73, QT65 are all poor suits to lead from, but KJ753 or QT864 would be wise.
- With a weak hand and no information from the auction, there is no point in establishing anything. The best bet is to hope partner has a better hand. In an attempt to establish partner's unknown suit, lead from the shortest suit.