I suggest reading https://donellameadows.org/archives/leverage-points-places-to-intervene-in-a-system
And my own note:
This isn't worst to best focus. Leverage points that need less effort also need greater movement to have an effect. Small movement at the greater leverage points does a lot.
But where to focus depends. The answer isn't always just to focus on the hardest-to-move points simply because any movement really has a major effect.