Around here our biggest job is to try to connect people that actually know about cycling with the people that make the decisions about the roads and paths and routes and all that good stuff.
Another job is to help the "powers that be" *and* the assorted subgroups of road and path users understand some of the sometimes counter-intuitive needs/wants of the other groups, whether it's "what are those cyclists doing on the streets when there is a sidewalk?" people or "we don't need bike lanes, just educate everybody!" people.
Perhaps mainly it's being present and visible ... one of our advocacy group's main goals is to help the general public perceive cycling as normal behavior (which is, of course, *not* the same as saying cyclists are normal people )