Terrorists thrive on causing chaos and carnage. A main focus from them is to take away the hope that others have for anything good to happen in life. We can't let them take that away. If we lose our hope, we lose the rest of the battle. So keep the flame alive. Keep in mind that there are good things in this world. There are good people in this world who want to do the right things. Keep hope that they will be able to make a difference. We can all make a difference, so that is another thing to do to keep hope. Do what you can to make things better, both for yourself and for others.
Finally, remember that the nasty people out there are few. They are loud. They are the minority of any group that they belong to. Have hope that the many many good people all over the world will speak up, speak out, and help keep hope alive.