Know and understand the process. Officials are busy with a variety of demands. Learn the decision-making process and the pressure points of the system. Use that pressure sparingly when you really need it. Plan and coordinate the action.
Continuity is vital.
Advocacy is a long-term commitment. Use a single spokesperson, whenever possible. Bring in technical expertise when needed, but don't cover the same ground repeatedly. Be there all the time. Effective advocacy is not part-time work.