Here's a great blog post from an MS Activist about how to do advocacy well: Effective Advocacy is Personal.
I really like how the author writes about the power of a personal story. It's so true that a legislator can oppose you on policy grounds, but they can't oppose your story. You may not win every time, but if you share your story, you can make a personal connection with that person, and over time, you'll win more often than you lose.
One of the reasons I came to work for the National MS Society is because of the opportunity I have here to tell stories that need to be told. When I was working in Olympia for a state senator, so rarely would we actually talk to someone impacted by the policies we were making. We'd talk to lobbyists, business leaders, executives, but rarely would we actually talk to the people whose lives were going to change because of these decisions that would be made. Imagine how different the world would be if people with MS had a seat at the table whenever laws were made that impact their lives. It's possible - we can do that. We just have to work together.