Charles Goren points out: „Defending against NT-contracts”

1. The lead

a. Attacking leads: Look first for an attacking lead in the partnerships longest, strongest suit.

b. Passive leads: When the contract is likely to be borderline, consider a lead, that will give nothing away.

2. Holdup in declarers suit
Hold up a winner in a suit that declarer must establish, provided this will not cost a trick.

3. Ducking (Blanko-Coup) in your (or your partners) suit
When endeavoring to establish a suit, consider ducking an early round in order to keep in touch with partner.

4. Entries

a. Protect or create partners entry, if he has the long suit.

b. Protect or create your entry, if you have the long suit

c. Destroy opponents communication by attacking their entries.

5. Unblocking
Avoid being left with a blocking card in your partners suit.

6. Shifting to a new suit
Consider a shift whenever the suit first led is unlikely to produce enough tricks.