You should also know that silence's CD is long enough that it's common practice in many fights to "rotate" silences. What this means is that you will use yours, then the PLD will use theirs, then you, etc.

To this end, it is helpful to make a macro that notifies your party when you use it, specifically with a sound effect. Just don't go overboard on it or it might get annoying.

The one I use on PLD is:
/micon "Spirits Within"
/ac "Spirits Within" <t>
/wait .1
/party "Silence used! <se.12>"

Feel free to adjust it for your needs. The wait is important, because you only need to hit it once for both the ability to go off and the message to immediately be sent after.