The first thing to reduce energy is to see where it is being wasted.

 An energy audit with blower door test and infared camera is the best place to start. 

 The list of upgrades range from adding insulation, to replacing HVAC systems and everything in beteen, such as new windows and doors to installing smart theromstats. But because each home is different and has different needs the only way to be sure your upgrades are right for your home is to start with an energy audit.