Rules for Leads After Play Begins

Declarer's the Boss, but . . . Once play has begun, declarer will in most cases set the pattern of play.

However, you and your partner will win some tricks, and so will face some lead situations after the opening lead. Some of the rules are the same as for the opening lead and some are different.   All are general guides to use only if there is no specific defense plan that can be advanced.  Your defense plan must always be foremost, as it's the only way you'll do well at defense, and defense is 2/3 of the game of Duplicate.

Some are defensive 'rules' -- so as not to give away anything.  Some are offensive -- to tap out a declarer or establish your tricks. All require you to think ahead in the play to anticipate the implication of each lead.

They rules are not in any sequence -- each applies sometimes, and you can't possibly obey all these 'rules' even if you remember all of them.  Generally, lead neutral cards if you can wait for the tricks 'due' your side but  lead attacking cards if you have to set them up.