Educate yourself. Dr. Childress' book, Foundations, is a relatively new resource for targeted parents. Also read the works of Dr. Richard Warshak and Dr. Amy JL Baker.
Attend a Parental Alienation Awareness Day local or national event. Volunteer for this excellent organization. For more information: http://www.paawarenessday.com
Spread the word about Parental Alienation. Use social media. Start a website. Organize. Start a Meetup group.
Tell your story. A lot of targeted parents are too embarrassed to admit that they are not seeing their children. Or they find it too painful to talk about. Believe me, I understand this. Tell your story anyway. Try to get media coverage. The world needs to know.
Go to court. Stand up for your rights as a parent. If you cannot afford an attorney, represent yourself pro se. You just may prevail. Even if you do not, you will help bring attention to the issue, and you will help to precipitate change.
Demand competence from mental health professionals counseling or evaluating your family. Although "parental alienation" per se is not an established standard of practice, the components of Parental Alienation are--namely, personality disorders, developmental trauma, the attachment system, family systems constructs, etc. Anyone counseling or evaluating your children must have competency in these areas.
Write the American Psychological Association, and ask them to officially recognize Parental Alienation.
Lobby for legislative reform. Here in the Activism section of this website I've provided examples of Parental Alienation legislation. Send letters to your state representatives asking them for similar legislation.
Sign this petition: http://www.petition2congress.com/3984/tell-congress-abolish-parental-alienation