Locally

Join a worthwhile campaigning group that has achievable short term goals and a place for you in it.
If you go to a meeting/bunch of meetings and you are not getting any useful or interesting work to do, please, come to us; we’ll give you worthwhile tasks that gradually build up your skills and confidence.

Learn more about the plans and (in)actions of Manchester City Council, AGMA
Via their own documents straight away if you’re feeling masochistic or first via these “bluffers guides” and THEN the documents themselves if you still have the will to live.