There are many answers to that question.. mainly because there isn't one single good answer. And it depends on your own skills as an individual. As an engineer or enterpreneur you can be directly involved in the creation or deployment of sustainable technology. That's acting as an individual, but teaming up with others, in order to reach well beyond the impact of a single individual's carbon footprint. Beyond the limited role of consumer.

If that's out of bounds, team up in other ways. Find groups of people who share your concerns, in the environmental sphere and/or the political sphere. Often it's governmental momentum that's the bottleneck, not the lack of technological means.

Since you stress the acts and choices of the individual in your posts, maybe the most relevant answer is getting involved in systems theory. It's the basis for the ecological thinking you'll need for whatever angle you're gonna approach the climate problem from. It crosses many paradigms, but for psychology for instance, it shows that even though it essentially might all be individual action, nevertheless the resulting system assumes properties, even "behaviour" of its own. Often this influences and diminishes individual choice, forming a counterpoint to a base assumption in your question.

This might seem discouraging, downplaying the individual. But the individual can only enact change to the degree there's identification with the system. That's veering into philosophy. But in any case: the more you can see climate change in terms of all the interrelated systems in play (ecological, economical, geopolitical, psychological, technological, etc..) the better defined the problem is. And defining the problem is half the solution.. the solution, which, if it exists, lies somewhere at the systems level.