It will help a lot if we stay sane and keep our wits about us. Our God is Reason, Justice, and Love. He gives us a peace beyond understanding. If we grow frenzied or despairing, people will think we are like the pagans, without hope in this world or the next.
God is always with us. We need to be with God. We need to pray often, and keep going to Mass. We need to support the Church and help our neighbors, as a response to God’s love for us. We need to fast and do acts of penitence, for sins of our own and of others. And we need to spread the Gospel, because people desperately need to know Jesus.