Attitude:

It is important to have some way to encourage or discourage partner in each suit.  This applies each time a suit is played (you won't always have the cards to show what you want but most of the time this will work).

A common system is Attitude (or Reverse Attitude).  Attitude is High to encourage and Reverse is Low to encourage - Using the reverse attitude method, defend the ♥ contract by leading the J♣ (partner may ovetake), A♦ next and play the 3♦ to say "continue" and win with the K♦ - no more tricks on offer here but you have ensured the tricks have been made.