Introduction to Bridge classes typically introduce students to the slogan “second hand low”. This slogan suggests that as a defender, when you are the second player to the trick, generally it’s best to play a low card rather than a high one. The underlying general principle is that, usually, it’s best to save your Aces and Kings so as to capture the opponents’ Queens and Jacks later. But bridge is not a “never or always” sort of game, so although usually it’s best to play low as second hand, it’s not always best.
For more information, see Real World Bridge 9: Defense.