In the US it's roughly a tie between road transportation and energy generation (which lumps together both heat and electricity).
(Source: University of Michigan https://css.umich.edu/publications/factsheets/sustainability-indicators/carbon-footprint-factsheet)
The global breakdown is similar: https://www.wri.org/insights/4-charts-explain-greenhouse-gas-emissions-countries-and-sectors
The solutions? Build mass transit, live in temperate climates, buy less stuff, ...? Honestly, I don't think we're not going to fix the problem with simple, local improvements (though by all means do what you can). There are global demographic forces to contend with. A century ago there were 2 billion people on earth. Now there are >8 billion, and in my lifetime we will surpass 9 billion. Many of those people are climbing out of poverty, and they want cars and air conditioners and all the other energy-intensive things that rich countries have enjoyed for a century. IMO we're going to need massive technological changes (like powering much of the world with nuclear very soon) in concert with a major population reduction and/or major changes to how people expect to live.