Preference carding by leader in NT
If after the 1st round you understand that leading suit has no potential, Discard, on the 1st opportunity a card in that suit. Your partner will easily understand that you don't want it any more...and that he should counter attack in another suit.
Additionally, the level of this discarded suit can be used as a preference signal.
- A high card to call for the highest suit remaining
- A small card to call for the lowest of the remaining suits
Conversely, if you discard another suit, your partner will understand that the leading suit is still of interest to you
Example
You are in south, leading against this NT contract. After leading the 5
♠ You understand the declarer has Ace King and Jack. He plays
♦ twice. What do you discard ?