Be Supportive. Let your friend know you are worried about the situation and why you think abuse is going on.
Be Understanding. Try not to judge your friend because it may be hard for your friend to believe he/she is a victim of abuse. It is frustrating to watch a friend go through unnecessary pain, but it must ultimately be your friend´s decision to get help and leave the relationship.
Be a Good Listener. Listen to what your friend tells you, and encourage your friend to get help through counseling.
Be Active. Stay involved with your friend´s life, so your friend does not feel so lonely and is if the abuser is the only person who cares what happens to him/her. Remain involved once your friend has the courage to leave the abuser because your friend will need continued support.