Looking at the makeup of CO2 emissions [1] (ignoring methane and other factors) it seems that it makes the most sense to avoid unneccessary heating and electricity consumption (which most people will already do because it's good for your wallet) and cut back on driving (which most people don't). For agriculture and industry, the two big other factors, you're probably right: There's not much a single person can do.

[1]: https://www.epa.gov/sites/production/files/2016-05/global_em...