Comfort the person with words of encouragement. Use common sense to offer words of support. Remember that intense emotional pain can be overwhelming, so be as gentle and caring as possible. There is no script to use in situations like these, because each person and each situation is different. Listen carefully, and offer encouraging words when appropriate.
Let the person know that you are deeply concerned. Tell the person that you are concerned, and show them that you are concerned. A suicidal person is highly vulnerable and needs to feel that concern.