Use prayer to help overcome sadness. Talk to the Almighty in your own language. Tell Him how awful you feel. Ask Him for the strength to cope with your present difficulties, and to grow from them.
-from Rabbi Zelig Pliskin’s “Gateway to Happiness,” p.180
While it is theoretically possible to develop an attitude to totally prevent sadness, the Jewish view is there are times when such feelings are appropriate.
For example, we have an obligation to cry over the death of another person. Also, we should care enough about potential suffering to pray that it will not come. And we utilize these situations as reminders to improve ourselves.
-Sources: from Chochmah Umussar, vol.2, p.203; Rabbi Zelig Pliskin’s Gateway to Happiness, p.172