What can astronomers do to influence political processes to help change national policies? What can astronomers do to encourage funding agencies, universities and observatories to implement more climate friendly actions? Influencing political processes or organisational systems is a complex task involving grappling with changing contexts and beliefs, multiple stakeholders and multiple interests. What is the most effective strategy the astronomy community can take to move from communicating about climate change and raising awareness, to supporting climate action and achieve system change? Drawing from several experiences addressing challenging policy topics and from the body of knowledge in political science on policy change, I outline a few key principles which astronomers can adopt to engage effectively with policy and organisational systems: first, develop deep contextual knowledge of decision making in policy systems; second, build strong networks including authentic partnerships across coalitions, and third, participate for long periods of time in the system. With these principles in mind, I outline a specific template for development of policy advocacy and communication plan