This is one of my favorite articles about advocacy. I certainly recommend a read.
The Elusive Craft of Evaluating Advocacy, by Steven Teles & Mark Schmitt
Very few big social changes happen without some form of advocacy. When these efforts succeed, the results can be transformative. Consider the recent expansion of charter schools or health care reform in the United States. Good ideas like these did not catch on widely just because they worked. They happened because of creative investments in public persuasion, legislative action, and political activity.
Most successful foundations and nonprofits understand the importance of advocacy. Over the last decade, foundations have put more resources into advocating for the policies they believe in, with some notable successes. Yet grantmakers have often hesitated to plunge in. Sometimes they worry about appearing too political or partisan. But more often they hesitate because effective advocacy is difficult, and evaluating whether various approaches are working is even harder.
Read more here.