Put a significant price on CO2 emissions (think like $300+/ton, instead of <$100), then tax every import from countries that take insufficient actions (or run a low CO2 emission price). Likewise, tax any export into countries that take no action.

Electrify everything where possible (especially transport and heating), get electricity CO2 neutral, get concrete and steel production CO2 neutral (lots of those would be an inevitable consequence of the emission pricing).

This would allow western democracies to basically fix the global situation on their own, by exerting economic pressure on developing countries (those want/need market access, like China).

It would make goods (and especially individual transport!) more expensive though (even if you re-emit the tax income), so you can be sure it's not gonna happen, because too many people are too selfish.

To add to the other replies, stopping animal agriculture would be a huge step forward.

Stop electing climate change deniers.

Stop listening to billionaires who don't want to pay - not to lose - a single cent to help reduce CO2 emissions, but are ready to pay millions to lobby against.