How would it be possible for the Polish-Lithuanian Commonwealth to not be a doddering puppet of Russia that gets eaten up by its strong neighbors?
My hypothesis is that preventing the rise of Prussia would be a start - it wasn't destined to become the dominant German state by the 19th century, let alone become the most powerful of the Protestant Imperial states. Also, a Russian loss in the Great Northern War would help, but with Sweden also having eyes on the PLC, this won't change a lot of matters.