In all situations at all times. Being gracious means to be kind, gentle, positive, helpful, and insightful. I work at a place where all the people around me are unbelievers. Their conversations are often vile, crass, filled with not so clean jokes. Don't be like the ungodly around you.
Salt prevents corruption.
God wants you to know how to answer everyone, v. 6. Speak the right word and the right time to the right person. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect. Part of having answers means being wise.