Any action you’d take to reduce release of CO2 in the atmosphere will help. So at home, for example, if your electricity comes from coal-fired plants, turn off unneccessary lights. In some part of the United States, it’s possible to choose where your electricity comes from; you can request that all your power be generated by renewable sources.
For more suggestions for simple ways to reduce your carbon footprint, visit Brighter Planet. On their website you can measure your footprint, track changes as you introduce them, and exchange info.